Theories of Formation of Coal. 109 



ceivable, but whether such enormous beds of limestone, with 

 the corals and molluscs which they contain, could be formed 

 in an estuary, may admit of doubt. But it is not so easy to 

 conceive tl\e very distinct separation of the coal and the stony 

 matter, if formed of drifted materials brought into the bay by 

 a river. It has been said that the vegetable matter is brought 

 down at intervals, in freshets, in masses matted together, like 

 the rafts in the Mississippi. But there could not be masses 

 of matted vegetable matter of uniform thickness 14,000 square 

 miles in extent, like the Brownsville bed on the Ohio (the 

 Pittsburg seam mentioned in page 170) ; and freshets bring 

 down gravel, and sand, and mud, as well as plants and trees. 

 They must occur several times a-year in every river ; but 

 many years must have elapsed during the gradual deposit of 

 the sandstones and shales that separate the seams of coal. 

 Humboldt tells us {Koswos, p. 295), that, in the forest lands 

 of the temperate zone, the carbon contained in the trees on a 

 given surface would not, on an average of a hundred years, 

 form a layer over that surface more than seven lines in thick- 

 ness. If this be a well-ascertained fact, what an enormous 

 accumulation of vegetable matter must be required to form 

 a coal-seam of even moderate dimensions ! It is extremely 

 improbable that the vegetable matter brought down by rivers 

 could fall to the bottom of the sea in clear unmixed layers ; 

 it would form a confused mass with stones, sand, and mud. 

 Again, how difficult to conceive, how extremely improbable 

 in such circumstances, is the preservation of delicate plants, 

 spread out with the most perfect arrangement of their parts, 

 uninjured by the rude action of rapid streams and currents 

 carrying gravel and sand, and branches and trunks of trees. 

 In the theory which accounts for the formation of beds of 

 coal, by supposing that they are the remains of trees and 

 other plants that grew on the spot where the coal now exists, 

 that the land was submerged to admit of the covering of 

 sandstones or shales being deposited, and again elevated, so 

 that the sandstones or shales might become the subsoil of a 

 new growth, to be again submerged, and this process repeated 

 as often as there are seams of coal in the series — these are 

 demands on our assent of a most startling kind. In the 



