246 ANALOGY TO COAL-MEASURES. [CHAP. XXXIV. 



rotting away, as must have happened in the case of 

 the celebrated fossil forest of Dixon-fold, in Lan 

 cashire, belonging to the ancient coal-measures.* In 

 the modern alluvial plain, also, river-sand will be 

 often thrown down, as the Mississippi shifts its 

 course over spaces on which pure vegetable matter 

 had been previously accumulating for hundreds or 

 thousands of years, just as we find sandstone some 

 times resting immediately upon the old coal-seams ; 

 and, if there be a long succession of downward move 

 ments, the thickness of strata, all formed in shallow 

 water or in swamps, may be indefinitely great. 

 Should the hilly country, moreover, be distant, pebbles 

 will no more be seen in the modern sand strewed 

 over the buried trees and layers of vegetable matter, 

 than they usually arc in the grits associated with the 

 coal of ancient date. The phenomena, also, of the 

 New Madrid earthquake, may help us to explain the 

 vast geographical area over which, in the course of 

 ages, dense fiuviatile and lacustrine strata, with in 

 tercalated beds of vegetable origin, may be made to 

 extend without any inroads of the sea. For the 

 inland parts of any hydrographical basin may be aug 

 mented indefinitely in length and breadth, while the 

 seaward portions continue unaltered, as the delta 

 around New Orleans, and the low lands bordering 

 the Gulf of Mexico, preserved their level unchanged, 

 while parts of Missouri and Tennessee were lowered. 

 By duly appreciating the permanent geographical 

 revolutions which would result from a succession of 



* Proceedings of Geol. Society, 1839, p. 139. 



