J.D.Dana wrote an excellent review of the geological overview of North Americacalled the, "Manual of Geology". Although this book is no longer a current textI found it very informative and the discussion much clearer of scientificjargon than later texts. Dana also has a broader and more inclusive feelfor this topic ie. he is not so narrowly focussed as later researchers.Dana makes very interesting observations regarding the coal beds in North America and this relates in particular to the problems of coal formation. What follows are excerpts from pp.309 to 321 of his text Manual of Geology.Dana's observations provide for me some difficult problems regarding the formation of coal specifically how do large trees become embedded not just inthe coal seam but in the sedimentary rock itself. How also do large rocksbecome embedded in coal seams if they are formed in peat bogs. Why also are suchextensive depths of limestone and sandstone and conglomerate rock foundwith coal seams? It appears to me that the coal was formed in very violentprocesses which moved these materials very quickly and crushed the biomasscreating coal. If coal is formed in slow coastal marsh processes how do largetrees "60ft long 3ft in diameter avoid being decomposed? see also the references to trees in coal in Morwell Australia
The thickness of the coal-measure rocks in these regions varies from 100 to 1000ft in the interior coal areas, to 4,000ft where greatest in Pennsylvania,and over 8,000ft in Nova Scotia....while in Nova Scotia, at the Joggins,there are according to Logan and Dawson, 14,750ft.
Stratification - The Carboniferous period opened with a markedchange over the continent. The Subcarboniferous limestones and shales, which had been formed upon submerged land, became covered with extensivegravel or pebble beds, or deposits of sand; and these, hardened into gritty rocks, made up the millstone grit and sandstone which underlie the Coal-measures. Similar conglomerates and sandstones wereformed afterward in the course of the Coalmeasures; but this rock is prominent for its extent, and for marking the commencement of the Coal era....The millstone grit extends over parts of some of the southern countiesof New York, with a thickness of twenty-five to sixty feet;...It occurs through all the Coal-areas of Pennsylvania, both the eastern and western;it is from 1,000 to 1,500 ft thick, about the centre of the anthracite region, and diminishes rapidly to the westward....
There is no fixed order of superposition. The following is an examplefrom western Pennsylvania, as published by Lesley: the beds are numberedin accordance with their succession, beginning below,-
feetA: Millstone grit ?
- Coal No.A with four feet shale 6
- Shale and mud rock 40
- CoalNo.B>(Of Mammoth bed of Central Pennsyl..) 3-5
- Shale, with some sandstone and IRON ORE 20-40
- Fossiliferous Limestone 10-20
- Buhrstone and IRON-ORE 1-10
- Shale 25
- CoalNo.C. The Kittanning Cannel 3.5
- Shale,--soft, containing two beds of coal, 1-1.5ft 75-100
- Sandstone 70
- Lower Freeport CoalNo.D. 2-4
- Slaty sandstone and Shale 50
- LIMESTONE 6
- Upper Freeport CoalNo.E. 50
- Shales 50
- MAHONING SANDSTONE 75
- COAL No.F. 1
- Shale; thickness considerable ?
- shaly sandstone 30
- Red and blue calcareous marlytes 20?
- CoalNo.G. 1
- LIMESTONE fossiliferous 2
- Slates and Shales 100
- Gray clayey sandstone 70
- Red marlyte 10
- Shale and slaty sandstone 10
- LIMESTONE-non-fossiliferous 3
- Shales 32
- LIMESTONE 2
- red and yellow shale 12
- LIMESTONE 4
- Shale and Sand 30
- LIMESTONE with bands of spathic IRON-ORE 25
- Pittsburg CoalNo.H. 8-9
The rock undelying a coal bed may be of either of the kinds mentioned;but usually it is a clayey layer ( or bed of fine clay ) which is called, the under-clay , Being frequently suitable for making fire-bricksuch beds often go by the name of fire-clay ....
In some cases, trunks of trees rise from it, penetrating the coal layerand rock above it....The rock capping a coal-bed may be of any kind, forthe rocks are the result of whatever circumstances succeeded; but it iscommon to find great numbers of fossil plants, and fragments or trunks oftrees, in the first stratum..... In sandstone layers, broken trunks of trees sometimes lie scattered throughthe beds. Some of the logs in the Ohio Coal-measures, described by Dr.Hildreth, are fifty to sixty feet long and three in diameter.....
In rare cases, an occasional boulder or rounded stone has been found in a coal-bed, as well as in other layers of the coal measures. E.B.Andrewsdescribes one of quartzite, lying half buried in the top of the Nelsonvillecoal-bed, at Zaleski, Ohio, which was twelve and seventeen inches in itstwo diameters. F.H.Bradley reports one, also of quartzyte, about four by six inches, found in the middle of the coal bed mined at Coal Creek, EastTennessee. These may have been dropped from the roots of floating trees, as are the masses of basaltic rocks occasionally found upon the coral atollsof the Pacific....
The iron-ore beds often contain remains of plants, in the form of stems and leaves; and the concretions, which are of siderite, and of very finetexture, often include portions of ferns, with even impressions of the hairs of the surface well preserved; and also remains of insects, Spiders,Centipedes, Amphibians, etc; all wonderfully perfect.....
The millstone grit, at the base of the coal-measures, in Pennsylvania, is mostly a whitish siliceous conglomerate, with some sandstone layers and a few thin beds of carbonaceous shale. It overlies the Subcarboniferousshale or sandstone. At Tamaqua, the thickness is 1,400ft; at Pottsville, 1,000ft; in the Wilkesbarre region, 200 to 300ft; at Towanda, Blossburg, etc., it caps the mountains, it is 50 to 100ft thick(H.D.Rogers).