38 ONTHE REVOLUTIONS OF 



and even the compact lime-stone in which we see the shells of our 

 layers embedded. Still less do we find that it deposits any portion of 

 those more solid and more flinty layers which preceded the formation 

 of shell-reefs. 



All these causes united would not perceptibly affect the level of the 

 sea, would not raise a single layer above that level, and assuredly 

 would not produce the least hillock on the surface of the earth. It 

 has been asserted, with some appearance of probability, that the sea 

 gradually decreases, and that observations to that effect have been 

 made on the shores of the Baltic* But whatever may be the causes 

 of these variations, it is certain that they are not universal ; that in the 

 greatest number of ports where there are so many persons interested 

 in observing the height of the sea, and when fixed and ancient works 

 afford so many means of computing these variations, the mean level is 

 constantly the same ; there is no general sinking ; there is no univer- 

 sal encroaching. In other places, as Scotland and various parts in the 

 Mediterranean, they have supposed, on the contrary, that the sea has 

 become higher, and now covers shores formerly above its level. f 



Volcanoes. 



The action of volcanoes is still more limited and more locally con- 

 fined than any others which we have adverted to. Although we have 

 no clear idea of the means by which nature feeds these fierce furnaces 

 so profound, we yet judge clearly, by their effects, of the alterations 

 which they have occasioned on the earth's surface. When a volcano 

 appears, after some shocks, some earthquakes, it finds an opening. 

 Stones and ashes are thrown far and wide ; lava is vomited forth ; the 

 more fluid portion glides away in long streams ; the more solid is 

 stopped at the edges of the aperture which it serves to elevate, and 

 forms a cone terminated by a crater. Thus volcanoes accumulate on 



* It is a prevalent opinion in Sweden, that the sea lowers, and that we can ford 

 or even walk dry-shod in many places where formerly it was impassible. Very 

 learned men have espoused this popular idea, and to so great an extent is M. de 

 Buch imbued with it, that he supposes that gradually the whole soil of Sweden will 

 become dry land. But it is singular that no regular and precise observations to con- 

 firm a theory broached so long, have been made, and made public, which would leave 

 no doubt, if, as Linnaeus says, this difference of level be as much as four or five feet 

 annually. 



■f* Mr. R. Stevenson, in his observations on the bed of the North Sea, and the 

 British Channel, asserts that the level of these seas has become constantly and sensi- 

 bly higher during the last three centuries. Fortis says the same thing of certain 

 places in the Adriatic ; but the example of the temple of Serapis, near Pozzuola, 

 proves that the borders of this sea are in many places of a nature occasionally to ele- 

 vate themselves and sink again. But, on the other hand, there are thousands of 

 quays, roads, and other places, made along the coast by the Romans, from Alexandria 

 to Belgium, the relative level of which has never altered. 



