136 DEPTH OF FRESH- WATER STRATA. [CHAP. XXXIV. 



sand strewed over the buried trees and layers of vegetable mat 

 ter, than they usually are in the grits associated with the coal of 

 ancient date. The phenomena, also, of the New Madrid earth 

 quake, may help us to explain the vast geographical area over 

 which, in the course of ages, dense fluviatile and lacustrine strata, 

 with intercalated beds of vegetable origin, may be made to ex 

 tend without any inroads of the sea. For the inland parts of any 

 hydrographical basin may be augmented 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 such earthquakes as that 

 of 181112, in the territory of New Madrid, we shall be pre 

 vented from embracing the theory implied in the language of 

 those who talk of &quot; the epoch of existing continents.&quot; In treat 

 ing of deltas, they are in the habit of assuming that the present 

 mass of alluvial matter which has been thrown into the sea at 

 the mouths of great rivers, began to be deposited in all the great 

 hydrographical basins of the world at one and the same fixed 

 period namely, when the formation of the existing continents 

 was completed ; as if the relative levels of land and sea had, 

 during that time, remained stationary, or had been affected to so 

 inconsiderable an amount, as to be unimportant in their influence 

 on the physical geography of each region, in comparison with the 

 changes wrought by the rivers, in converting sea into land. But 

 what we already know of the deltas of the Po, Indus, Ganges, 

 and other rivers, leads to a very different conclusion. The bor 

 ing of an artesian well at Calcutta, was carried to the depth of 

 481 feet, the greater part of the section being below the level of 

 the sea, and yet all the beds pierced through were of fresh-water 

 origin, without any intermixture of marine remains. At differ 

 ent depths, even as far down as 380 feet, lacustrine shells, arid 

 a stratum of decayed wood, with vegetable soil, which appears to 

 have supported trees, was met with.* These appearances may 

 * See &quot; Principles of Geology,&quot; Seventh Edition, 1847, p. 266. 



