1893.J evidence for the Recurrence of Ice Ages. 227 



mum height is the total thickness without allowing anything for 

 the folds, or for the vast masses of older strata pushed up at the 

 same time. 



Again after a somewhat commensurate interval during which 

 the folds are planed off and the edges of the Carboniferous Rocks 

 with their Devonian basement are exposed, the direction of move- 

 ment is again changed, and all goes down to receive the great 

 Jurassic system with its Poikilitic basement series, and so the story 

 is repeated again and again. 



We have taken one district on the margin of the Atlantic 

 basin for an approximate estimate of thicknesses and of therefrom- 

 inferred amount of upward and downward movement. But the 

 same reasoning holds everywhere along the axes of principal dis- 

 turbance, and here and there some members of the series are 

 enormously thicker than their representatives in the sections I have 

 referred to. For instance, in the central basin of Scotland the 

 lower division of the Old Red Sandstone is said to have reached a 

 depth of more than 20,000 feet, while in North Germany the Coal 

 Measures attain a similar thickness. The Alps and Pyrenees offer 

 proofs of upward and downward movement along axes of yielding 

 at many successive periods down to late Tertiary times. As Le 

 Conte^ has shown, sediment is apt to be thicker and evidence of 

 earth movements greater along the axes of mountain ranges ; still 

 there have been wider submergences and elevations, as proved by 

 the vast thickness of sediment such as those of which examples 

 have been given above, and these are more important as showing 

 the instability of the continental areas. 



Heim has shown that the crumpling up of the Alps has 

 reduced the breadth of the sediments of which it is composed at 

 least 120,000 metres or 74 miles and, though his figures have 

 been questioned by later observers, all admit an enormous re- 

 duction of their original horizontal extent'"'. More recently it has 

 been suggested that the upper part of an immense fold of rock has 

 been carried from the districts south of Mont Blanc and Monte 

 Rosa to the northern slopes of the Alps, and that the movement 

 extended all along the northern edge of the Swiss and Bavarian 

 Highlands^. 



Every author who has described the Alps and given us sections 

 across them bears witness to the vast extent of the earth move- 

 ments that have recurred there down to quite late times. For 

 this we have only to look at the sections of Alphonse Favre, 

 Renevier, and many others, besides the more recent observations 



1 Journal of Geology, i. 1893, p. 544. 



^ Heim, Mechanisnius der Gebirgsbildung, Vol. ii. 1878, p. 213. 

 3 Schardt, " Sur I'origine des Prdalpes liomandes," Arch, des Sciences Phys. et 

 Natur., Dec. 1893, Geneva. 



