546 CENOZOIC TIME — MAMMALIAN AGE. 



chatel to the Juras. The Alpine heights are in many places deeply- 

 grooved, on a magnificent scale, to a height of 10,000 feet above 

 the sea (as well seen in the valley of the Aar), showing that this 

 was the height of the ancient glacier in the mountains, — while its 

 depth or thickness must have been 4000 or 5000 feet. The slope 

 from Mt. Blanc to the Juras back of Neufchatel averages very 

 nearly one degree, — equivalent to one foot in sixty. There are 

 other blocks in the Alps still larger than the Pierre-a-bot. One of 

 them, at Steinhof, near Seeberg, contains 61,000 cubic feet, and has 

 travelled from its original site nearly 200 miles. 



These facts from Switzerland seem to be but a repetition of those 

 observed in connection with the Drift epoch in America and other 

 regions. They will be better appreciated after a perusal of the 

 pages on Glaciers under the head of Dynamical Geology. 



The Glacier theory most satisfactory, but the Iceberg theory required, in 

 some cases, for the borders of Continents. — In view of the whole subject, 

 it appears reasonable to conclude that the Glacier theory affords the 

 best and fullest explanation of the phenomena over the general 

 surface of the continents, and encounters the fewest difficulties. 

 But icebergs have aided beyond doubt in producing the results 

 along the borders of the continents, across ocean-channels like 

 the German Ocean and the Baltic, and possibly over great lakes 

 like those of North America. Long Island Sound is so narrow 

 that a glacier may have stretched across it. 



In Europe icebergs were evidently more extensive in their opera- 

 tion than in America. Glaciers have probably continued there in 

 action from the time of their first appearance on the continent to 

 the present day ; and the Glacial era on that continent may not, 

 therefore, be the well-defined period that it is in North America. 



Geography. — The Glacial epoch an epoch of high-latitude elevation. — 

 The evidence presented with regard to an epoch of unusual cold in 

 the early Post-tertiary, when glaciers and icebergs prevailed vastly 

 beyond their existing limits, leaves little doubt that the epoch was 

 one of some increase of elevation throughout the drift or cold lati- 

 tudes. The elevation may not have affected every paft, but yet 

 was sufficient to make the northern and southern hemispheres 

 alike in their glacial phenomena. This evidence is strengthened by 

 the fact that fiords occur in the same latitudes, north and south. 



The author's views on fiords and the epochs of the Post-tertiary 

 period were first published in the Amer. Jour. Sci. [2] vii. 379, 

 1849, and xxii. 325, 346, 1856. 



See further, on Glaciers, Appendix D. 



