NATURAL HISTORY OF THE EIGHTEENTH CENT. 411 



tion consists likewise of several different kinds of rock, such as grey- 

 wacke, trap, transition limestone, etc. These rocks also contain fossils, 

 but the animals belong only to the lower orders in the scale, and are 

 of species which no longer exist. The knowledge of the Floetz forma- 

 tion is more limited, and it is found in level countries where all the 

 strata are for the most part below the surface. The rocks of this for- 

 mation are the old red sandstone, limestone, gypsum, trap, coal, basalt, 

 greenstone, etc. The Alluvial formation consists of loose soil, gravel, 

 sand, moss, etc. The Volcanic formation comprises the lavas, ashes, 

 etc., ejected from volcanoes. 



This imperfect sketch of the Wernerian system of geology will serve 

 to indicate the most notable differences between it and a rival theory 

 which was originated in Britain by JAMES HUTTON (1726 1797). 

 Hutton was born in Edinburgh, and was educated for the medical 

 profession, but after having taken his degree at Leyden, he returned 

 to Edinburgh, and resolved to live upon the means which he had in- 

 herited from his father in order that he might devote himself to the 

 study of nature. He was a man of great industry, and he traversed 

 many parts of England and Holland in order to study the geological 

 phenomena. His views were first published in a paper contained in 

 the "Edinburgh Philosophical Transactions " in 1788, but afterwards, 

 1795, they were more fully developed in a separate treatise. This was 

 an epoch-forming treatise, for it was the first in which geological 

 changes were referred to causes whose nature and mode of action are 

 identical with those still operating. 



The diagram in Fig. 186 will serve to exemplify the Wernerian views 

 of the structure of the earth which were prevalent in England up to the 

 time of the publication of Hutton's paper in the "Edinburgh Philoso- 

 phical Transactions," and before the appearance of his book in 1795. 

 The lowest known stratum of the earth was believed to be granite, and 

 the highest mountains in the world were supposed to be composed of 

 it, or at least the great central nucleus of their principal chains. Por- 

 phyry, trap, whinstone, slate, and basalt were all held to be varieties 

 of granite, all being supposed to have been volcanic productions that 

 have been exposed to different degrees of heat. It was admitted that 

 the greater part of the stratified rocks had been deposited as sediment 

 from water. Speculations dealing with the remotest condition of our 

 planet and of our system supposed that our sun might have itself been 

 originally a planet revolving about some still greater luminary which 

 has long since dissipated its heat and light, but about which our system 

 may still revolve. The earth, it was suggested by some of the more 

 speculative geologists, was probably projected from the sun as a semi- 

 fluid mass, which by cooling became superficially solid, at least, and 

 at length its temperature so far decreased that many substances, at first 

 existing only as vapour, were condensed into the liquid or solid form. 

 Thus the watery vapour condensing into water formed the ocean. 



