GEOLOGY OF THE WESTERN ALPS. 151 



change is much too sudden. He points out the resem- 

 blances of the rocks of the Prealpes and those of the zone 

 of Brianconnais, and concludes that they were once con- 

 nected by a great sheet of rocks belonging to this zone, 

 which completely covered the two intervening zones (those 

 of Mont Blanc and the Limestone Alps). It had previously 

 been suggested by Bertrand and Steinmann that the Pre- 

 alpes were the remains of a great arch like that here 

 suggested. But instead of the arch having risen to the 

 south of the area, as Schardt concludes, they thought that 

 it rose to the north. In that case it would have formed 

 a oreat mountain rano;e over Northern Switzerland. This 

 has been accepted by many geologists, and named by 

 Giimbel the " Vindelecian Chain " (fig. 1 ). Schardt, how- 

 ever, shows that there is nothing to the north that could 

 represent the other limb of the arch. He therefore accepts 

 the arch, but makes it cover Southern, instead of Northern 

 Switzerland. 



This view has been attacked from two sides. One of 

 the points the great arch has been conjured up to explain 

 is the occurrence of huge blocks of granite in the Flysch of 

 the hills on the north side of the Lake of Thun. Some of 

 these are in size fifty metres cubed. Some of them are so 

 large that they have even been described as intrusive 

 granites. M. Sarasin (3) has studied these- boulders in 

 detail, and shown that their existence is fatal to, and not 

 explained by Professor Schardt's theory. The boulders 

 occur in four zones : those ^of the lowest, or the zone of 

 Ormonts, are familiar to all visitors who ascend the Niesen, 

 on the south side of Lake Thun ; the highest occurs 

 typically at Habkern, on the north side of the same lake. 

 Sarasin shows that the materials in all of them have come 

 from the south, and not the north, but that those of 

 different zones have come from different areas. He con- 

 cludes that at the beginning of the Eocene the region of 

 the Prealpes was occupied by a series of arms of the sea 

 parallel to the Alpine chain, and separated from one an- 

 other by islands of Jurassic rocks. In these arms of the 

 sea were formed the breccias of Ormonts and the Niesen, 



