Acknowledgment:  Various persons have forwarded the information herein (as noted in the text or under photos) ...

 

This webpage looks at some of the effects of surface heating - various examples are given/discussed and the writer (John Byrnes, geologist - john.mail "@" ozemail.com.au would like to hear from others who know of similar things; and especially to receive more photos for this compilation.    The writer first became interested in the ability of soil to sometimes melt from surface heatings after seeing many examples of 'soil slag' in the district between Wellington and Molong, New South Wales.   Such melted material might be a combination of tree ash material plus admixed 'soil', or especially the 'soil' carried into trees through the influence of termites.  However, there have been no "before and after" type observations that would indicate just exactly how the Wellington-Molong district material (which is usually found as isolated specimens)  did form. 

Heating can come from the strike of lightning, the impact of large bodies from outer space or even from nuclear weapon explosion (thankfully rare).   More commonly the heating source is the combustion of tree wood, or shallow coal seams.  Combustion of peat would presumably also leave fused products although no example of this is at present known to the writer.  Human-made haystacks may burn and leave glassy residue, and in one case a mass of slag of uncertain exact genesis was found at the site of a major city fire.  Human-buried biomass might also burn to leave fused residue - or at least a case described by Thy et al. (1995) suggests this (a 5-inch thick layers of glassy slag interleaved with ashy soil found in an ancient midden not thought to be associated with pottery or iron making).  Consideration of that slag suggested that temperature in the range of 1155-1290°C had occurred in order to fuse whatever the buried garbage/biomass had been.  At that occurrence slag layers encompass several hundred square meters, so the phenomenon is not a trivial one.

Lightning may itself fuse soil but more importantly is thought to often be the trigger for many cases of such "combustion metamorphism".

The present writer first met with relatively common/widespread fused combustion products in the area between Wellington and Molong.   Examples are described herein but unfortunately photos of such material are not at present available to add here.   It is darker in colour and more durable than "wood-ash stone" and is highly vesicular (often resembling the porous nature of termite mound interior, in appearance) and quite light-weight.   Pieces of it have sometimes been found in unusual places, like in cracks atop of limestone outcrop (near Nubrigyn Creek, west of Stuart Town) .    The material has been  well known to many local landowners.   A few have regarded pieces of this "soil slag" as "meteors", or as material hurled long distances from volcanoes (residents of this area generally are aware that there used to be volcanoes around, e.g. to the south near Orange).   On the other hand, other landowners, perhaps most of those who are familiar with the material, think it results from wood/tree fires.   One farmer stated that he'd seen it left at the site of a large wood fire, at a time when some of the remnant wood was still smouldering.   One occurrence of the material was on the shores of the Macquarie River and was thought to be where a large log-jam has formerly existed and had caught fire and burned.   

The soil that fused here is primarily composed of clayey arkosic sand (quartz, microcline and a small amount of plagioclase), with trace amounts of calcite, hornblende, and augite.  There is considerable clay content.   In 2005 it was theorized by Los Alamos National Laboratory scientist Robert Hermes, and independent investigator William Strickfaden, that much of the glass was formed not simply by sand which was exposed to the fireball, but the sand which was drawn up inside the fireball itself and then rained down in a liquid form.  Rounded pearls are found which returned to solid form before hitting the ground.   The glass layer was generally 1-2 cm thick, with the upper surface marked by a very thin sprinkling of dust which fell upon it while it was still molten.  At the bottom is a thicker film of partially fused material, which grades into the soil from which it was derived.   Some of the material is extremely vesicular with the size of the bubbles ranging to nearly the full thickness of the specimen.

According to a man named Dr Ralph Pray who has since operated a metallurgical research laboratory for 39 years, in Monrovia, Calif., he took it on himself to "clean Up" the melted sand, and he took it to Verne Byrnes, a mining engineer in Santa Fe.   Pray wrote as follows:

 

 

Wind-blown sand still uncovers sun-bleached bones of men and mules dead for centuries along New Mexico's Jornado del Muerte, the waterless hell where Spaniards died traveling between Santa Fe and Chihuahua. Few large areas in the United States can match its barren, flat desolation. Flat, barren, desolate, a waterless hell of windblown sand . . . and at its center, a slight depression in the ground, marking the place of man's first great insult to the earth: Trinity Site, Ground Zero of the first explosion of an atom bomb. Here, on the sands of New Mexico, at 5:29 a.m., July 16, 1945, the bomb went off, vaporizing the massive steel tower that held it and melting the sand at its feet into a carpet of green glass. For a radius of more than 100 feet melted sand in the form of green glass covered the desert like a splotchy carpet shining in the light from above, dull by night, bright by day. This monument to man's inhumanity to man, the largest blur on the landscape, was surrounded by a high fence, tight strands of barbed wire, a locked double gate and multilingual warning signs. Then the powers that had built the site abandoned it. But the glass endured - a splotchy green circle 200 feet in diameter, dull by night, bright by day, a monument to man's inhumanity to man. This monument was surrounded by a high fence, tight strands of barbed wire, and multilingual warning signs. The gate in the fence was chained with three padlocks - two put there by government agencies - serving as links in the chain. If you got through any of the three, you could gain admission to Trinity Site. And that's what I did. In July, 1951, I entered the site, and I took the glass. Let me explain. Federal agencies had been sponsoring an annual trek to worship at Trinity, and the green disc of radioactive glass was there for innocents to pray over. While living in the remote desert of northern New Mexico I had seen an aerial photograph of the site in a popular magazine. It looked like a giant scab. It was an impurity waiting to be taken away. Writers wrote about it. I was determined to remove it without a trace of publicity. My self-appointed task was to gain entry to the government glass and haul it off for burial, to repair the desert, clean away the radioactive afterbirth. I was in the Army at the time - a draftee stationed at the Guided Missile School at Ft. Bliss, Texas. My buddy, Jesse Petty, a fellow draftee from Carrizozo, New Mexico, went to the unguarded site, melted one of the links with his gas torch, and put his own padlock in its place. Jesse had volunteered, "I'll go out there and cut the chain for you and put on a new padlock, but I won't go in there, not for anything." My plan was to drive a truck to the site, use my key to open the lock, remove the radioactive glass called Trinitite, and transport it to the Los Alamos area for proper burial. Los Alamos, New Mexico, was the place where the bomb was produced. It would leave from the beautiful desert and go back where it came from. I bought a used red pickup truck at El Paso Dodge. For money, I used my army pay and profits from weekend sales in Santa Fe of silver filigree jewelry and other items bought in Juarez, across the bridge from El Paso. One Saturday, after electronics lab at the army missile school, the truck took me north through Alamogordo and Carrizozo, then west. I followed Jesse's map and turned south off the lonely highway onto a thin blacktop road speckled with deep chuckholes. The sand blown over the road showed no sign of tire marks. There was nothing, no one, for many miles. I was used to the army, the noisy barracks, months of technical lectures, hundreds of men. Where was everyone? Was I crazy?                   The author stands in the slight depression generated by the the first atomic bomb explosion.. 'Now I become Death, the destroyer of worlds.' Those were the words that Robert Oppenheimer, Director of the Los Alamos Laboratory, wrote about the first minutes after the blast. Perhaps these words drove me; perhaps they were the guiding force behind my mission. I could remove the obvious signs of the first destruction, clean up the mess, do more than just leave tire tracks in the sand. The road and the poles led to the fence, to the locked gate. I parked and fished the keys out of my army fatigue jacket. I examined the chain and visualized General Groves, Manhattan Project Manager, confidently snapping the army padlock shut. "Sorry, General, to go around you, but we're not quite finished here." My key worked. Good old Jesse. I swung the double gate open and drove in. There was the glass! It was certainly not attractive. It was a scattering of dull, hardened goop. As I drove to its center, the sound of my tires on the virgin glass was like breaking soda crackers. The small depression at ground zero was maybe a foot lower than the surroundings. I saw a concrete pier sticking out of the sand. It was the stump of one of the four tower legs. No other trace of the 100-foot tall, heavy steel tower remained. One thing I would need was a screen to separate the sand from the glass. If I shoveled the glass onto a screen hanging steeply off the side of the truck, it would slide into the truck bed, and the sand would fall through the screen and onto the ground. I drew up the plans for a folding screen that would be attached to the truck and visited an El Paso hardware store for the parts. A rake would come in handy too, if I wanted to make little piles of glass for the shovel. (second trip) I drove in and got to work. I raked little piles of Trinitite to the center of thirty-foot circles and shoveled the stuff onto the screen. The glass slid into the truck, and the sand fell through. Fine. I did ten circles with about fifty pounds in each.      Pray sieving out Trinite to remove it.  The melted sand had the color of Coke bottle  glass and the brittleness of ice. At 500 pounds the little truck had a load. There was plenty of Trinitite left for future trips. "Who gets the glass?" We turned west on the blacktop highway to Socorro. "It'll end up with Verne Byrnes, a mining engineer in Santa Fe. He's in charge of the burial detail." "How do you know him?" I could picture Verne with his little pot belly. "He owns the Pennsylvania Mine in the Cerrillos Mountains. Two years ago, I was working a mine nearby and helped bail the water out of the Penn shaft. Santa Fe's not crowded. You get to know everybody. You'll see." We went through Albuquerque and continued north. Santa Fe was my favorite city in the U.S. There was nothing remotely like it. We dropped off the Trinitite, spent a wonderful night in Santa Fe, and drove back to the base Sunday night. I decided to go in for the rest of the glass after dark. Raking and shoveling in darkness would be a problem, but I thought that a flashlight taped to each handle might do the trick. I fashioned a hood and slitted mask out of cardboard for each headlight of the truck; then, late on a Friday night, I began my first nocturnal trip, alone now, and anxious. Human life, however, continued to be in short supply. My tire tracks from the previous week were the only ones in the sand at the gate. I entered and got to work. The flashlights guided the rake and shovel. I loaded about 600 pounds and was back on the highway at 4 a.m. I reached Albuquerque by seven and unloaded in Santa Fe a few hours later. Two more trips were needed to remove the bulk of the glass. I did these alone and in darkness. I preferred it. The stress was minimal. I liked the cool night air. Seeing the wild animals in this place recently dedicated to total destruction gave me some hope for the future. It was almost as if they knew something. A few days after my fourth trip, a telephone call from Santa Fe warned me that my destination in the city was under observation, possibly by federal authorities. The word was out. That ended the Trinitite Project. As for the stuff I removed, it was buried in 55-gallon drums near Los Alamos, where it belongs. When I look at the photos, however, I see someone other than myself. I was never that crazy, I think, even fifty-some years ago. But I'm glad it happened. I wish everyone knew that man's greatest shortcoming is the pride he holds in his weapons, and that instruments of death wouldn't be needed if we all did what we should to get along better. If we fail to practice international brotherhood, what remains of Trinity Site, this speck of a surface scar, may someday become the most hated place on earth. ( Abridged from http://libertyunbound.com/archive/2003_07/pray-groundzero.html and http://www.mine-engineer.com/mining/trinity.htm )

 

 

 

EFFECTS ASSOCIATED WITH BUSHFIRES AND BURNING VEGETATION (TREES, WOOD, GRASS; HAY)

Some examples below are after the fires of  7-2-2009 near Yarra Glen and Marysville, in the Victorian bushfire tragedy.

Fire storm of 7th February 2009, as seen from Yarrs Glen.

The Billabong Bridge burning, near Yarra Glen.  (Photo: Al White)

 

Common effects of fire on stone (spalling etc.):

At this memorial rock at Yarra Flats Billabongs, near Yarra Glen, there had been Lilydale toppings on one side of the rock and mulch

on the other side.   The blackened area around the rock is where the burning mulch generated a high level of heat, and the rock

shattered or spalled in places.  (Photos: Barry Sheffield)

 

Effects on fire have been long known, and used in the past to work and harden stone.

 

Flintknapping is today more than a fringe hobby in the USA.   It has grown a very strong following to the point where there is quite a number of individuals who might actually be making a living from it (?).   In order to improve the "knappability" of a number of diferent kinds of rock (mostly cherts) the rock is heat treated.  The effects of heat treatment often include colour change.   Experimention into the effects of heat on rock is widespread.  There are presumably academic studies on the matter (not yet located) but general experimentation with kilns, turkey roasters or other methods of heating is probably widespead.

 

One good introduction to flintnapping and 'stone cooking' is by Tim Mayeux at http://www.geocities.com/tlmayeux :

 

 

Tim writes: "A long time ago, the Natives on this Continent learned a wonderful technique.  They found that many types of their favorite tool making stones were much easier to work after being heated.  How this was discovered is anyone's guess.  Perhaps some chunks of flint were mistaken for cooking stones and placed in the campfire.  Possibly a forest fire came through a flint rich area and burned over the rock.  Who knows?  What's important is that many stones that would otherwise be almost impossible to work are vastly improved by proper heat treatment.  The stone usually turns glossy, more waxlike in texture, more brittle, and sometimes a dramatic change in color occurs.   However, heat treating does have a down side. Sometimes rock can be overcooked, causing it to crumble, or pot-lid. It can also become so brittle that it is very difficult to work without breakage.  Therefore, a fine line must be walked when heat treating. Depending on whether the stone is in chunks, spalls, blanks, or slabs, and whether the stone is to be used for percussion work or pressure flaking will determine the amount of heating required for a particular stone. "

 

Tim's webpage on "Cooking Rocks", at http://www.geocities.com/tlmayeux/cooking.html gives details about treatment of various varieties.  Some general guidelines are given.   First, lighter colored stone generally can take more heat than darker colored stones ("The exception seems to be Silicified Ash").  Thinner pieces such as slabs and blanks can take higher temperatures than chunks and spalls.   This has to do with the stone getting too hot too quickly on the outside of larger pieces while the inside is still relatively cool.   Tim notes that can cause the stone to break apart of worse still to actually burst or explode.   A lot has been discussed about hold time, or the amount of time that stone is held at the target temperature.   In Tim's experience, hold time is more crucial for big pieces, where it may take a while for the middle to reach the target temperature.  Tim notes that hold time also seems to be a factor in colou change.   Some dramatic changes in the colour of stone occur by holding at the target temperature for as long as three days.

 

Cherts may generally be heat treated at 450-500 degrees.  Or blanks and spalls 400-450, but they also might take 500.  Foir some varieties, people think 425-450 gives a tougher stone for percussion.   Some slabbed chert may usually take 500-600 degrees heat treatment, and some coarser-grained cherts may take higher temperature of 700 degrees.   Novaculite (a form of 'chert') is noted for taking the highest temperature heat treatment.  Spalls and blanks of novaculite can start at 750, and Tim likes 800 for most of the white and porcelain-like varieties.  Some people like 850 or even 900; however novaculite may get very brittle and glasslike at such higher temperatures.

 

On the other hand McCarthy, F.D. “An Analysis of the Large Stone Implements from Five Workshops on the North Coast of New South Wales” in Records of the Australian Museum 21:8 (1947) pp.411-430 shows the efforts of T. Dick to try and photograph re-creations of Aboriginal customs for posterity.   No less than five of Dick's photos illustrated the placing of pebbles onto a fire to fracture them.   However McCarthy doubted that this was former practive there.   No collected implements showed any sign of having been in the fire, McCarthy noted.  McCarthy thought that the evidence appears to "rule out the employment of the heat-fracturing method in the old days".

McCarthy also stated that the effect of fire on chert was actually to soften the stone.  That much is contradicted by Tim's webpage information as noted above. 

 

 

More effects of fire (with examples from Victoria):

 

 

Destroyed railway tressle built in 1888 at Yarra Glen.  (Photo:  'Haminator')

 

 

 

 

Burned timber railway trestle bridge, near Yarra Glen.  The soil has turned orange in a burned out post hole and 

next to burned timber.   Also the ballast stone has been burned orange.   (Photos: Barry Sheffield)

 

 

An example of soil turned orange.   This is in  the bush near Marysville (Timm's tramway area).  It is in an area not particularly intensely

burnt by comparison with some others in the district, but still pretty well crisped.  Fire occurred on 7 February 2009.  There were plenty

of large dry logs on the forest floor to burn once the fire front had passed but the fire left no obvious effects on the soil apart from

numerous examples of soil turned orange in colour, as in this photo.  In this example most of the body of the stump has simply

disappeared, including many of the former roots which are now discernable only as cavities.

(Photo and information: Peter Evans)

 

 

 

This burned area is the remains of where round hay bales were stacked side by side.  Most of the river flats that were burnt now
have lush green grass growing on them, but where hay bales burnt is still just blackened ash.  Near Yarra Glen.

(Photo: Barry Sheffield)

 

Fused materials may result from wood pile fires, bushfires or from the slow burning of large hollow trees.   The material which has fused may have been largely carried into the trees by termites in many cases.   However, in "wood ash stone" there is little admixed 'impurity' in the melting of wood ash. 

"Wood-ash stone".   Note wood impression on right side. Bar scale 1 cm.   (Source:  Humphreys et al., 2003. 

Location not stated, but Humpheys et al. 1987 have reported such near Sydney.)

Under certain conditions the burning of trees results in the production of copious amounts of carbonate minerals such as calcite and rare potassium carbonates.  Known as ‘wood-ash stone’ or ‘fused wood-ash stone’, it is thought to result from the fusion and recrystalisation of ash within the trunks of large standing trees that caught fire higher up the trunk and slowly burnt downwards.  This burn pattern appears to favour the conversion of wood to ash concentrated in alkali and alkaline-earth metals and thence to wood-ash stone under a slow-burning regime.  Wood-ash stone was first reported from North America in several conifers ((Englis and Day 1929; Kienholz 1929; Milton 1944; Milton and Axelrod 1947), and deciduous angiosperms (Dawson and Sabina 1958; Mandarino and Harris 1965; Dietrich 1971). It was first reported in Australia in Angophora costata (Myrtaceae), a prominent evergreen tree species in the Sydney area, by Humphreys and Hunt (1979) and Humphreys et al. (1987).  This represented the first report of wood-ash stone outside North America. All these records refer to the natural occurrence of woodash stone.  The finds near Sydney were in Lane Cove National Park.

 

Humphreys et al. (2003) describe buetschliite stone, or wood-ash stone. as resulting from the combustion of wood and the fusion of mostly alkali and alkaline-earth compounds.   Such has been reported from North America and Australia in a variety of conifers and angiosperms.   In most cases it occurs within the trunks of trees that have slowly burned downwards (Kienholz 1929).   The resulting mass of stone, often in excess of 20 kg, is normally an off-white colour and may contain inclusions of charcoal.  Often the cast of wood and flow structures are present.  Apart from carbon and oxygen the main elements present are Ca and K with lesser and more variable amounts of Mn, Mg, Na and P, which matches the composition of wood-ash.     Calcite [CaCO3] has been recorded in all samples subjected to mineralogical testing but rare potassium-calcium carbonates also occur.  Buetschliite [K2Ca(CO3)2] and kalcinite [KHCO3] have been reported from North America (Milton & Axelrod 1947, Dietrich 1971).   Australian samples exhibit appreciable calcite and in one sample a carbonate involving Na, K and Ca.  In addition, there may be minor substitution of Mg /Fe in the calcite and the possible presence of dolomite and aragonite, small amounts of periclase (native magnesia, MgO) as well as quartz, which occurs mostly as sand-sized grains.   The presence of buetschliite, calcite, portlandite [Ca(OH)2] and periclase has also been reported in furnace slag deposits where wood chips have been used as fuel providing that temperatures do not exceed about 750^oC (Mistra et al. 1993, Olanders & Steenari 1995).  The same slag material heated to 1300^oC revealed a variety of silicates in the presence of sufficient Si.   

Fallen burnt tree trunks often reveals a central core of baked soil. This soil originates as infill deposited by termites, such as Coptotermes spp. in south-east Australia. Humphreys et. al (2003) stated that this soil when baked is typically crumbly, white to orange in colour and consists of clay with variable amounts of finer quartz sand that sometimes resembles fired pottery fragments.

Baker and Gaskin (1946) reported examples of trachyte and basalt with smooth glassy surfaces, inclusions of carbonised wood and impressions of wood tissue.  The basalt examples were found within and at the base of a burnt tree, which indicates that the required secondary phase of partial fusion occurs during bushfires.

In addition fired haystacks can yield silica-glass (straw-silica) fragments that in appearance resemble other silica glass such as fulgurites and tektites but differ in the lower silica but higher RO and R2O content (Milton & Davidson 1946).  Other examples of silica-glass from Macedon and also Darwin glass were attributed to burning trees by Baker and Gaskin (1946).  The low content of silica in most trees makes this  unlikely unless the termite-introduced mixture of clay and sand is present.

   Fire effects  (Humphreys et al. 2003)

The most commonly occurring soil iron oxides are haematite, goethite and maghemite.  At soil temperatures in excess of 400ºC Fe-rich substrates, in the presence of a reducing agent such as organic matter, may generate large quantities of fine-grained maghemite.  Fire may therefore lead to increase in magnetic susceptibility and saturation isothermal remanent magnetisation values (by up to three orders of magnitude).  

 

 

The 1929 work of Kienholz described; plus the erroneous idea that such 'clinker' may be a meteorite.

(Source:  Milton and Axelrod, 1947)

 

 

Phil feeding logs into the 100-year-old mining boilers at Sovereign Hill, Victoria.  Ordinarily, these burn logs 5-ft long and 6-10 inches in diameter. However, bark is often raked up from the log yard and burned as well.  In raking up the bark some mineral material must inevitably get mixed in too (mud, small stones etc).   Formed in these boilers are "pizza" shaped bodies of a bubbly slag, often with stones incorporated into it.  These have to  be raked-out when the grates are cleaned as they obstruct the passage of air.   Peter

Evans has seen the same slag in boilers burning sawdust  from Mountain Ash (E. regnans). Temperatures in the furnaces

of these boilers range from 800-1000 degrees Celsius.    (Photo and information:  Peter Evans)

 

 

Boiler slag from the Sovereign Hill boilers   (Photo:  Peter Evans)

 

 

Geological Survey report GS1975-178, dating a fusion event in  the Dripstone area at 860 +/- 100 BP.  

 

Geological Survey report GS1981/526 noting the occurrence of melted surface material (soil) at seven localities in NSW.

 

 

FUSION RESULTING FROM BURNING OF COAL OR OIL SHALE

North Dakota clinker 

All who travel through western North Dakota may noticed reddish layers and brick-like masses of baked and fused clay, shale, and sandstone that color and shape the landscape.  These baked materials, known as clinker (or locally as "scoria"), formed in areas where seams of lignite coal burned, producing heat that baked the nearby sediments to a form 'natural brick', 'slag'  and 'clinker'.   Clinker beds typically range from a few feet to 50 feet or so thick in western North Dakota, but much thicker beds are found in Wyoming and Montana.

The first known reference to such clinker is by William Clark who, while he and Meriweather Lewis were navigating the Missouri River in 1805, made the following entry in his journal (when they were wintering at Fort Mandan,  March 21, 1805):

"Saw an emence quantity of Pumice Stone on the sides & feet of the hills and emence beds of Pumice Stone near the Tops of them, with evident marks of the hills having once been on fire. I Collecte Somne of the different sorts i.e. Stone Pumice & a hard earth, and put them into a funace, the hard earth melted and glazed the others two and the hard Clay became a pumice Stone glazed."

Soon afterwards, on April 16, 1805, Meriweather Lewis wrote the following:

"I believe it to be the strata of coal seen in those hills which causes the fire and birnt appearances frequently met with in this quarter. where those birnt appearances are to be seen in the face of the river bluffs, the coal is seldom seen, and when you meet with it in the neaghbourhood of the stratas of birnt earth, the coal appears to be presisely at the same hight, and is nearly of the same thickness, togeter with the sand and a sulphurious substance which usually accompanys it."

After Lewis and Clark, some other explorers explorers believed the clinker beds had a volcanic origin.  Lewis and Clark had it right though, in their excellent appraisal of how the clinker had formed from the burning of lignite beds.

Partly melted, fused mass of vesicular clinker at HT Butte.   (Photo:  Bob Biek)

Rugged badlands carved from rocks ranging in age from Late Cretaceous through Eocene occur along the Little Missouri River in western North Dakota, USA.  Layers of colorful clinker are widespread throughout these badlands, as has been described by John P. Bluemle.

REFERENCES:

 

Bluemle,   J.P., North Dakota's Badlands  NORTH DAKOTA NOTES NO. 12.  North Dakota Geological Survey.

Bluemle,   J.P., North Dakota's Clinker  NORTH DAKOTA NOTES NO. 13.  North Dakota Geological Survey.

The sedimentary layers exposed in the Little Missouri Badlands are mainly continental sediments that were deposited by rivers and streams flowing east to the Dakotas from the Rocky Mountains in Montana and Wyoming at the time of the Laramide orogeny. They consist of layers of poorly lithified siltstone, claystone, sandstone, and lignite coal that were deposited in a coastal plain environment. River, floodplain, and swamp deposits predominate. Bluish gray layers of weathered volcanic ash form excellent marker beds in places and brownish gray layers of sand containing thin, orange, iron-rich bands also form prominent markers.

Lignite is common.   A one-metre-thick bed of lignite might have resulted from a 10-m layer of peat and some of the lignite layers are more than 10 m thick.   Besides decaying and helping to form lignite, some trees have been silicified and preserved standing upright on some horizons.   Few studies have been done on the petrified wood, but because of the abundance of leaves associated with the stumps, it is inferred that many are the remains of the Dawn Redwood, Metasequoia. 

   

 

Stump at Petrified Forest Plateau, Theodore Roosevelt National Park.   (Photo:  Bob Biek); and another

Petrified stump seen in situ in Theodore Roosevelt National Park (Photo: J. Bluemle)

Also common are reddish bands of clinker, formed when some of the lignites burned.  Exposed lignite seams may catch fire when they are struck by lightning, when prairie fires burn over them, or they may ignite spontaneously.  The baking and fusion products range from only mildly baked sediments, in which original sedimentary textures and structures (even fossil leaves) are preserved, to glassy slag.   Variants include vesicular, frothy material reminiscent of volcanic scoria, and very hard conchoidally fracturing porcellanite.  The clinker is most commonly reddish in color, but it varies from black to the palest pink.

The most extensive of these is the HT Butte clinker, which marks the contact between the Bullion Creek and Sentinel Butte Formations in places where the HT Butte lignite bed has burned.  The HT Butte clinker deposit is as thick as 15 m in some exposures.   A thin layer of white ash, mostly potash, lime, and other inorganic incombustible minerals, is typically found at the base of clinker beds.  The ash bed alters along joint to bentonite.

The clinker is thought to develop by repeated, comparatively small, discrete burns.  Several early explorers reported coal fires in the northern Great Plains region, and over recent years, range fires have ignited lignite beds many times.  In two places in western North Dakota, in Theodore Roosevelt National Park and near Amidon, lignite seams were recently burning for many years.   A seam of lignite at Buck Hill in the park burned from 1951-1977.   During early October, 1976, prairie fires that burned over several areas of southwestern North Dakota ignited underground lignite seams in at least 30 locations over a 7,000-acre area near Amidon.  Again in July, 1988, a number of lignite seams were ignited during widespread fires in the badlands.  Sometimes the lignite fires are ignited by juniper tree roots burning down from the surface into the coal.  Over the years, such a large number of lignite seams have burned, over such a broad area, and under such a variety of situations, that it seems likely spontaneous combustion has been responsible for many of the fires.  Lignite that contains a high percentage of sulfur is especially prone to spontaneous combustion.    The presence in the lignite of the minerals pyrite and marcasite (forms of iron sulfide) plus moisture results in the production of heat.

 

FUSION RESULTING FROM OTHER TYPES OF FIRE

This lump of slag is all that remained, at site of a former hardware store, after the Great Fire of 1877, 

at St. John - the "Black Wedsnesday" fire of June 20, 1877.  (Photo:  Saint John & Fredericton )

 

The Great Fire or Black Wednesday fire in St John's history happened in 1877 and leveled two-fifths of the city, an area of almost one  square kilometre.

The huge blaze could be seen that evening from Fredericton, more than 100 kilometres away.    The main business centre in what had been one of the most prosperous cities in North America was wiped out.   Businesses throughout the uptown city area began emptying their safes and taking the contents to the Bank of New Brunswick, not dreaming that such a large stone building could burn down.  People everywhere were evacuating and trying to save possessions; but in places the bundles of goods tossed from second-storey windows were on fire before they reached the hands of those who stood below to try and catch them.

Within nine hours, the blaze reduced Saint John's downtown and South End to an unbroken landscape of smoldering ruins.    More than 1,600 homes were destroyed and the fire obliterated most public buildings and businesses.   Lost were the the post office, city hall, customs house, five banks, 14 hotels, 14 churches,  as theatres and schools.  Some 1,500 commercial and industrial buildings  were razed included 10 retail grocers, 116 liquor dealers, 93 commission merchants, 80 law offices, 55 boarding houses, 55 shoemakers, 36 tailors, 32 flour dealers, 29 insurance agents, 29 clothing stores and 22 dry goods establishments.   Some 15,000 people were left homeless. 

Black Wednesday came following a three-week hot dry spell, with the temperature hovering about 25 deg  C.   A breeze had come up that morning and developed into a stiff wind.  This was to be a fateful wind but at first it was seen as a relief to many of the city's 50,000 heat-enduring residents.    

Nobody knows for sure what happened but the major theory is that a spark  from the unbaffled smokestack of the Kirk and Daniels lumber mill was carried by this wind to nearby Fairweather's Hay Storage barn (where the present day Hilton Hotel stands.

About 2 O'clock in the afternoon the the fire alarm went and firemen went to combat the breaking-out fire.  At that time it seemed far from the principal streets, and people took but little notice, thinking it would soon be extinguished.   But soon the wind or gale wasblowing sheets of flames and sparks from building to building.    The firemen ran for their lives along Dock Street, pulling their fire engines behind them.    In some locations, fire horses had to be quickly cut loose from their engines, lest they be killed by the great   heat.   More companies of firemen arrived, but only to see the wind-blown flames leaping high and possibly unstoppable.   Men lingered as long as they could in their struggle to save buildings, but all had to retreat eventually.   Many of the firemen were holding boards to shield their faces against the heat, as their clothing was being singed.

( http://new-brunswick.net/Saint_John/greatfire/greatfire3.html )

 

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