566 GEOLOGY. 



that they were drifted by moving waters from one place to another. 

 (4) The layer of rock next overlying a coal-bed often contains abundant 

 remains of vegetation, especially in its lower part, as if the condi- 

 tions which brought about its deposition resulted in the destruction 

 of the forest growths which had preceded. In such situations, trunks 

 of trees 50 and 60 feet long, and 2 or 3 feet in diameter, are sometimes 

 found. (5) The vegetable matter in and about coal-beds is made 

 up of the trunks, small stems, leaves, and fruits of the various plants 

 concerned, intermingled in such manner as to indicate that the vegeta- 

 tion grew where the coal now is. The drifting together of vegetation, 

 while it would not have completely separated these various constitu- 

 ents one from another, could scarcely have left them commingled as 

 they are now found. 1 



While it is confidently believed that most of the workable coal 

 represents the growth of vegetation in situ, it is not to be understood 

 that 1 ; coal was : never formed from vegetation which drifted together, 

 or that " drifted " vegetation never entered into the formation of coal. 

 In some of the small coal-basins of France, much vegetation washed 

 down from the land is said to have entered into the coal, 2 and the 

 same may be true elsewhere. 



We have now to inquire in more detail concerning the conditions 

 under which the coal-beds were formed. The things to be accounted 

 for are three: (1) The conditions under which the necessary bodies 

 of vegetation accumulated, often essentially free from the admixture 

 of sediment; (2) how it was kept from decay; and (3) how it was 

 changed into coal. 



Swamps and marshes are the only places where vegetal matter 

 is now accumulating in quantity, with little admixture of sediment. 

 Where swamps are large, or where their surroundings are sufficiently 

 low to prevent the inwash of sediment, vegetation is accumulating, 

 uncontaminated with any notable amount of sand or mud. In the 

 marshes along some parts of the Atlantic coast, for example (Fig. 253), 

 there are great quantities of vegetal matter which is locally mixed 

 with little sediment. Likewise in Dismal Swamp, vegetable mattei ; 



1 For expositions of the theory that the coal-plants grew where the coal is found 

 see Logan, Trans. Geol. Soc, VI, 1842, p. 495; Newberry, Am. Jour. Sci., XXIII 

 1857, p. 212, and Geol.. of Ohio, Vol. II, p. 125. 



2 Geikie, Text-book of Geology, 3d ed., p. 808. 



