Ixvi PEOCEEDIK^GS OP THE GEOLOGICAL SOCIETY, 



Von Waltershausen has further been bold enough to investigate 

 and state the mean temperatures of different regions of the earth's 

 surface in early geological epochs, beginning with the Silurian. He 

 argues that this may fairly be attempted only on the supposition of 

 a slow and uniform change in one dii-ection, in accordance with the 

 theory of Fourier, and on the assumption that a much larger pro- 

 portion of the earth's surface was covered with sea in those early 

 times than at present, when the ratio of dry land to sea is about 

 2 to 5. 



The calculation has to be based on that hotly disputed and still 

 very uncertain element, the thickness of the earth's crust, which, 

 taking the mean density of the earth at 5*67, and the mean specific 

 gravity of lavas at 2-912, derived from the depth where the rigid 

 and the fluid constituents would be in contact, he estimates at about 

 66 miles Enghsh, or -^th of the earth's radius. 



Upon this foundation several curious tables are calculated, show- 

 ing what would be the temperature of the surface with a given 

 thickness of solid crust, at what depth, in each case, the boiling- 

 point of water would occur, and the mean temperature of the dif- 

 ferent latitudes at the epoch of the several geological formations. 

 But in their application these results are vitiated by the author's 

 having ignored the presence of stratified formations beneath the 

 Silurian ; and the comparatively recent discoveries of Sir William 

 Logan have sufficiently proved to geologists the enormous errors 

 which may result from our imperfect knowledge of the stupendously 

 thick and long continued deposits which have preceded the forma- 

 tion of what we were accustomed to consider the lowest series of 

 truly sedimentary rocks. 



Eeturning, however, to safer ground, the Baron examines and 

 rejects the various theories which have been brought forward to 

 explain the evidences of the former great extension of glaciers in 

 the Alps. Influenced by the Lyellian doctrines, he is no believer in 

 the catastrophic action which many authors have connected with 

 the upraising of that great chain of mountains, but requires a long 

 period of time for the gradual elevation of the entire mass, begin- 

 ning near the end of the Tertiaiy period, when the Molasse and 

 Nagelfluhe had abeady been deposited. When the main range at 

 this time began to emerge from the waters, a long gulf or arm of the 

 sea lay stretched along the north side of the Alps, which, as may be 

 seen from the geological maps, extended westward round to Mar- 

 seilles, and eastward away beyond Vienna into Hungary. All the 

 larger lakes of Switzerland and of the Bavarian highland are sitiiate 

 in this zone. As the higher parts of the ridge rose into the region 

 of perpetual snow, the formation of glaciers began, the streams of 

 which would come to an end when they descended to a stratum of 

 atmosphere having a mean annual temperature of about 2° E. 

 (36°'5 F.). "Whilst, then, this arm of the sea remained at its original 

 level, it would have a mean temperature of at least 10° E. (54°-5 F.), 

 and the lower end of the glaciers would be still from 3500 to 4700 feet 

 above the water-level. Oscillations seem to have taken place, as in 



