150 



ON THE ORIGIN OF COAL-FIELDS. 



lakes and shores of the sea near the mouths of great rivers were elevated and laid dry, 

 they would present us with a gradation of similar phenomena, from the decaying drift 

 wood recently lodged in the subaqueous surface, to the half-carbonized vegetables, 

 perhaps even down to coal itself, the result of plants having been entombed in mud and 

 sand from the earliest period, when the rivers in question began to flow 1 . 



Pursuing his investigations in descending order, the inquirer at length finds, that 

 throughout the whole succession of sedimentary strata, there exists the same analogy ; 

 and that wherever the beds contain many impressions of plants, coal of one description 

 or other is as constantly associated. Commencing in the tertiary period, when the re- 

 lations of the land and sea were approaching to their present condition, we have many 

 proofs of similar accumulations. Thus the deep gorges and river valleys which run into 

 the recesses of the Alps, may be cited as clear and well known examples ; for in these 

 we find carbonaceous matter piled up in alternating layers of sandstone and shale, (the 

 sand and mud of former days,) on which are impressed the forms of various vegetables. 

 Some of these deposits, containing fluviatile and terrestrial shells, were evidently heaped 

 up by rivers or in lakes | while others, at lower levels on the mountain sides, pass 

 under strata charged with marine remains little differing from those of the present sera. 

 This stage of the inquiry presents to us the surface of the globe in some degree diver- 

 sified by continents like our own, and hence the plants from which the coal of this 

 period was formed, though differing specifically from recent vegetables, are analogous 

 to them in general aspect. (Dicotyledonous Plants.) 



Descending through the upper secondary formations, we recede to periods when 

 all the animals and plants contained in the strata are dissimilar from those of existing 

 nature, but still we have occasional proofs of dry land in terrestrial, lacustrine, and 

 fluviatile accumulations alternating with marine deposits. The freshwater shells and 

 land-plants of the Wealden — the fossil flora of the lower oolitic formations (Yorkshire 

 and Brora), are examples familiar to geologists. 



In the portions of the globe hitherto examined, these last-mentioned aeras appear on 

 the whole to have been little productive of vegetables, and hence we find the amount of 

 coal in deposits of this age to be small. As far as our present data enable us to 

 speculate, it would appear that the plants of these formations, differing essentially from 

 those above the chalk, have an intertropical character, which some geologists conceive to 

 be a proof of the existence of smaller continents than those of the more modern periods, 

 the lesser degree of cold arising from an insular surface, suiting such a vegetation ; but 

 we must not forget that the flora in question has been collected only in Europe, and 



5 See some excellent apposite remarks by Dr. Fitton on other collateral geological features, which the 

 northern part of the continent of America would present, in case it were now sunk beneath the sea, so as to 

 lodge a sheet of marine strata upon the surface of the present terrestrial and freshwater accumulations. (Geoi. 

 Trans., vol. iv. p. 325.) ' 



3 Examples, — Styrian Alps, Gratz, &c. Sedgwick and Murchison, Geol. Trans., vol. iii. p. 301. 



