J.D.Dana wrote an excellent review of the geological overview of North America called the, "Manual of Geology". Although this book is no longer a current text I found it very informative and the discussion much clearer of scientific jargon than later texts. Dana has a broader more inclusive feel for this topic he is not so narrowly focussed as later researchers. Dana makes 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 some difficult problems regarding the formation of coal specifically how do large trees become embedded not just in the coal seam but in the sedimentary rock itself. How also, do large rocks become embedded in coal seams if the seams are formed in peat bogs. Why also, are such extensive depths of limestone, sandstone, and conglomerate rock found with coal seams? It appears to me that this coal was formed in very violent processes which moved these materials quickly and crushed the biomass creating coal. If coal is formed in slow coastal marsh processes how do large trees "60ft long and 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 marked change over the continent. The Subcarboniferous limestones and shales, which had been formed upon submerged land, became covered with extensive gravel 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 were formed afterward in the course of the Coal measures; 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 counties of 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 example from western Pennsylvania, as published by Lesley: the beds are numbered in 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-brick such beds often go by the name of fire-clay ....
In some cases, trunks of trees rise from it, penetrating the coal layer and rock above it....The rock capping a coal-bed may be of any kind, for the rocks are the result of whatever circumstances succeeded; but it is common to find great numbers of fossil plants, and fragments or trunks of trees, in the first stratum..... In sandstone layers, broken trunks of trees sometimes lie scattered through the beds. Some of the logs in the Ohio Coal-measures, described by Dr.Hildreth, are fifty to sixty feet long and three feet 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.Andrews describes one of quartzite, lying half buried in the top of the Nelsonville coal-bed, at Zaleski, Ohio, which was twelve and seventeen inches in its two 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, East Tennessee. These may have been dropped from the roots of floating trees, as are the masses of basaltic rocks occasionally found upon the coral atolls of 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 fine texture, 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 Subcarboniferous shale 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).