28 Account of the 



find that we can do no more than rest upon some general ex- 

 pression of great undefined magnitude. 



^ The surface of the country was next destined lo be covered 

 by a different class of materials, not vmiversally, perhaps, as in 

 the former case, but partially through its whole extent ; for the 

 fresh- water deposits are met with at intervals in every part of 

 the region we are now considering. Vast lakes of still water must 

 have spread over the country, and must have covered at least all 

 the land that is lower than the summit of the Esquiline Hill, 

 that is, 150 feet above the bed of the Tiber, for at that eleva- 

 tion fresh-water deposits are found ; and it is, moreover, proba- 

 ble that they occur at a much greater elevation in the neigh- 

 bourhood of Tibur, independently of those formed by the Anio. 

 That such inland seas of fresh water did exist, there can be no 

 doubt; but it is impossible to form a conjecture by what barrier 

 they were contained on the side of the Mediterranean, unless we 

 suppose a ridge of limestone hills parallel to the Apennines, af- 

 terwards swept away, and of which the Circean Promontory and 

 the hills behind Civita Vecchia are the remains. That the wa- 

 ter of these lakes rested upon the surface of the country for 

 many ages, is proved by the great thickness of the beds of tra- 

 vertino, which, in stagnant water, would be deposited much 

 more slowly than in those cases where rapid evaporation takes 

 place, as in the motion of water charged with extraneous matter. 



The draining off of these lakes, if it took place suddenly, 

 would cause much abrasion of the land, and probably by this 

 operation the present surface of the country was fashioned. 



Changes in the relative level of the sea and land have been 

 alluded to. By what probable causes were these changes effect- 

 ed ? The answer that most naturally occurs to such a question 

 is, that it was the sea which changed its level ; but farther in- 

 quiry makes it much more probable, nay almost certain, that it 

 was the " fixed earth " which moved, and that the " unsettled 

 sea" remained unaltered. No permanent partial change in the 

 level of the sea can take place*. If it rose at any time to the 



• " No river can put forward its delta, without raising the level of the 

 whole ocean, although in an infinitesimal degree ; and no lowering can take 

 place in the bed of any part of the ocean, without a general sinking of the 

 water, even to the antipodes." — Lj/ell, 474. 



