1 64 VARIETY OF DEPOSITS DUE TO RIVERS. 



the shore at Nice the depth is 2000 feet; but in the Adriatic, where 

 it receives the sediment of the Po and other rivers in the upper part, 

 the greatest depth is 22 fathoms. Yet from the abrupt borders of 

 the hill ground within the area of the sedimentary land, it is inferred 

 that the Adriatic must formerly have been a deep gulf. 



Nature of the Deposits in Gulfs, Estuaries, &c. Farther from 

 the influence of the rivers the depth increases considerably. Donati, 

 on dredging the bottom of the shallow portion of the Adriatic, found it 

 to consist partly of mud, and partly of calcareous rock, enclosing shells. 

 The form of these sedimentary deposits must be what in common lan- 

 guage is called horizontal, the substance of them is fine clay and calcareous 

 matter with shells ; and as the ratio of accumulation is nearly uniform, 

 there will be little appearance of stratification, unless the calcareous 

 deposits be formed at intervals. If by any effort of upheaval this 

 bed of the Adriatic should hereafter be elevated and made dry land, 

 as so many other extensive tracts along the borders of the Mediterranean 

 have been, we should have an argillaceous deposit similar to the 

 London clay, and perhaps identical with the subapennine marls, 

 except for some difference in organic remains, and of such an area as 

 would appear incredible to those who believe in the almost slumbering 

 condition in modern times of the mechanical and chemical forces 

 which modify our globe. The same conclusions might be derived 

 from an examination of the mouths of the Rhone, Volga, Danube, 

 Ganges, Euphrates, &c., which enter the sea under the same favour- 

 able circumstances, and transport enormous quantities of fine sediment 

 into comparatively tranquil and now shallow waters. A river like 

 the Mississippi, which hurries along an enormous volume of deep 

 waters, and preserves its velocity to the edge of the sea, discharges a 

 prodigious quantity of matter, which settles round its many mouths 

 into a vast and growing delta. But the kind of matter here deposited 

 and the mode of its arrangement will be different. Forests matted 

 together by the growth of ages, with all their foundations, their 

 alligators and other inhabitants, are swept down by this mighty 

 stream, and either embedded for a time among its winding and vari- 

 able channels, or hurried into the sea, and there agitated, and partially 

 or completely separated into beds of earthy and of vegetable matter ; 

 and thus the Gulf of Mexico is now filling with deposits, which 

 in no uncertain way simulate carboniferous strata. We are in- 

 formed by Lyell, whose volumes are full of valuable information on 

 all subjects connected with the modern operations of natural agencies, 

 that a great part of the new deposit at the mouth of the Rhone consists 

 of calcareous and arenaceo-calcareous rock, containing broken shells of 

 existing species ; and Admiral Smyth ascertained that over the broad, 

 very gently inclined bed of this growing delta, marine shells were 

 occasionally drifted by a south-west wind. In this way alternations 

 of fresh-water and marine shells may be occasioned, in which the 

 marine portions will predominate towards the sea and the fresh-water 

 part be most decided toward the land. 



The shorter and more rapid the course of a river, the larger and 



