478 SCIENCE PROGRESS. 



1857. It would lead us too far to discuss this important work 

 as fully as it deserves; but it is necessary to notice one or two 

 points on which the views adopted by Rothpletz are by no 

 means those which are generally accepted. On the much- 

 debated question of the origin of the Schlern dolomite in 

 Southern Tyrol, he sides with those who of late have 

 attacked the views so strongly advocated by Mojsisovics. 

 He believes that this great mass of dolomite owes its 

 formation to alga^ and not to corals. 



On another question of general interest he has much to 

 say. He discusses the work of Heim on the Glarnischer 

 Alps, and comes to the conclusion that the double fold 

 which figures so prominently in our text-books has no 

 existence. The Lochseitenkalk which forms the middle 

 limb of the northern fold in Heim's section, and which 

 Heim believes to represent the Jurassic rocks dragged out, 

 is according to Rothpletz nothing but a fault breccia, with a 

 certain amount of vein material. The plane along which 

 we find the Lochseitenkalk is a great thrust plane. 



The most important result of a change of view of this 

 kind is that it reduces very considerably the amount of 

 contraction which it is necessary to suppose that the Alps 

 have undergone. According to Heim, 1 in the Northern and 

 Central Alps the beds which, folded as they now are, occupy 

 a breadth of 82 kilo., would, if flattened out, spread over a 

 width of 158 kilo. Rothpletz arrives at a very different 

 result. The actual width of the Alps in his section is 222 

 kilo.; while, if the beds were unfolded, it would be 271 '5. 

 Thus the contraction is only 18 per cent., instead of nearly 

 50, as Heim's figures would give it. The two writers are 

 treating of different areas, but Rothpletz believes that 

 Heim's result is due to error in his interpretation of the 

 folds. 



The earth-movements which gave rise to the Alps 

 took place at various periods. They certainly began in 

 pre- Permian times, and continued at intervals until at 

 least the Miocene period. In the Western Alps, near the 



1 Mechanismus der Gebirgsbildung, vol. ii., p. 213. 



