Ch. I] VOLCANIC KOCKS. 5 



between the creation of man and tlie deluge. They liave imagined 

 that the antedihman bed of the ocean, after having been the receptacle 

 of many stratified deposits, became converted, at the time of the flood, 

 into the lands which we inhabit, and that the ancient continents were at 

 the same time submerged, and became the bed of the present seas. 

 This hypothesis, although preferable to the diluvial theory before alluded 

 to, since it admits that all fossihferous strata were successively thrown 

 down from water, is yet wholly inadequate to explain the repeated revo- 

 lutions which the earth has undergone, and the signs which the existing 

 continents exhibit, in most regions, of having emerged from the ocean at 

 an era far more remote than four thousand years from the present time. 

 Ample proofs of these reiterated revolutions will be given in the sequel, 

 and it will be seen that many distinct sets of se iimentary strata, hundreds 

 and sometimes thousands of feet thick, are piled one upon the other in 

 the earth's crust, each containing peculiar fossil animals and plants of 

 species distinguishable for the most part from all those now living. 

 The mass of some of these strata consists almost entirely of corals, others 

 are made up of shells, others of plants turned into coal, while some are 

 without fossils. In one set of strata the species of fossils are marine ; 

 in another, lying immediately above or below, they as clearly prove 

 that the deposit was formed in a lake or brackish estuary. When the 

 student has more fully examined into these appearances, he will become 

 convinced that the time required for the origin of the rocks composing 

 the actual continents must have been far gi-eater than that which is con- 

 ceded by the theory above alluded to ; and likewise that no one 

 universal and sudden conversion of sea into land will account for geo- 

 logical appearances. 



We have now pointed out one great class of rocks, which, however 

 they may vary in mineral composition, color, grain, or other characters, 

 external and internal, may nevertheless be grouped together as having a 

 common origin. They have all been formed under water, in the same 

 manner as modern accumulations of sand, mud, shingle, banks of shells, 

 reefs of coral, and the like, and are all characterized by stratification or 

 fossils, or by both. 



Volcanic rocks. — The division of rocks which we may next consider 

 are the volcanic, or those which have been produced at or near the sur- 

 face whether in ancient or mod'-3rn times, not by water, but by the action 

 of fire or subterranean heat. These rocks are for the most part unstrat- 

 ified, and are devoid of fossils. They are more partially distributed than 

 aqueous formations, at least in respect to horizontal extension. Among 

 those parts of Europe where they exhibit characters not to be mistaken, 

 I may mention not only Sicily and the country round Naples, but Au- 

 vergne, Velay, and Vivarais, now the departments of Puy de Dome, 

 Haute Loire, and Ardeche, towards the centre and south of France, in 

 which are several hundred conical hills having the forms of modern vol- 

 canoes, with craters more or less perfect on many of their summits. These 

 cones are composed moreover of lava, sand, and ashes, similar to those 



