322 SCIENCE PROGRESS. 



schists to have been brought upon the top of the newer 

 beds by means of a thrust-plane, the whole difficulty dis- 

 appears. A thrust-plane, however, like any other divisional 

 plane in a mass of rock, must be affected by any foldings 

 which may take place subsequently in that mass ; and in 

 the Toulon area the gliding surface is not now a true plane, 

 in the mathematical sense of the word, but has been thrown 

 into a series of anticlinals and synclinals which run nearly 

 east-west. 



A much more striking instance of a thrust-plane, the 

 evidence of which, however, is not so clear, has been 

 brought forward by Schardt (32). The northern zone of 

 the Alps consists of ranges of hills which lie in front of the 

 main chain and which are often spoken of as the Limestone 

 Alps or Pre-Alps. Geographically this zone is continuous, 

 but geologically the portion which extends from the Chab- 

 lais (south of Lake Geneva) to the Stockhorn (west of Lake 

 Thun) is quite distinct from the south-west and north-east 

 parts of the zone, which are known respectively as the 

 Faucigny and Unterwald. The folds of the Alps of the 

 Faucigny and Unterwald are not the continuations of those 

 of the Chablais and Stockhorn, and the thrust-planes which 

 are present in the latter 1 are unknown in the former. 

 Moreover the character of the rocks is different, and 

 Schardt looks upon the Pre-Alps between the Chablais and 

 the Stockhorn as a mass of foreign rock which has been 

 brought from the south upon a gigantic thrust-plane. He 

 places the original position of this mass in line with the 

 Rhaetikon (on the Austrian border), and considers it pro- 

 bable that the thrust-plane may be a continuation of that 

 of the Rhaetikon. 



Lugeon (22) in a somewhat earlier paper gives a dif- 

 ferent explanation of the structure of the Chablais. He 

 supposes that the beds of that area were thrown into a 

 dome, which bulged out at the sides and was pinched in at 

 the base, so that all around the edge the beds were reversed 



1 In another paper (33) Schardt gives sections of the Pre-Alps near 

 Montreux on the northern shore of Lake Geneva. 



