182 GLACIAL HISTORY. 



and the areas of distribution of the blocks are indicated upon it 

 by means of shadings of longitudinal fine lines and dotted lines. 

 But it must be borne in mind that the erratic blocks are very 

 irregularly distributed, and that in the plain of Switzerland there 

 are large spaces in which none of these blocks are found. For 

 instance, in many portions of the low ground there are no blocks, 

 or they occur very sparingly ; whilst they may be met with up to 

 considerable elevations on the sides of the hills and mountains. 

 In the lateral dales of the lower part of the Canton of Valais and 

 about the Lake of Geneva they extend up to several thousand 

 feet above the bottom of the valley. 



In the Jura the boundary of the blocks forms a remarkable 

 curve, the highest part of which may be found about opposite 

 to the middle of the basin of the Lake of Geneva. On the 

 Chasseron, to the north-west of Yverdon, the curve of blocks is 

 3100 feet above the valley-bottom (1400 metres, or 1531 yards, 

 above the sea); at the Chaumont it is 2400 feet above Neuchatel, 

 at the Chasseral 2000-2200 feet, and near Orvin 700 feet, sink- 

 ing near Soleure into the low ground. The western part of the 

 curve reaches the bottom of the valley at Gex to the north-west 

 of Geneva. 



Similar phenomena are met with in Eastern Switzerland. In 

 the Canton of Zurich there are vast accumulations of blocks of 

 Alpine limestone, sernifite, and granite near the Gyrenbad (2400 

 Paris feet above the sea), and almost up to the summit of the 

 Bachtel ; they are found on the entire chain of the Albis to the 

 Uetliberg, and also upon the chain of hills fringing the right 

 bank of the Lake of Zurich from Pfannenstiel to the Zurich- 

 berg. At the Lagern, in the Canton of Zurich, the blocks ex- 

 tend to within a few hundred feet of the ridge of the mountain. 

 The hills surrounding the Lake of Constance are, in several 

 places, dotted even to their summits with erratic blocks; and 

 similar blocks are found on the hill of Hohentwiel in the 

 Hohgau. 



The rocks from which the whole of the materials of the Erratic 

 formation have been derived are quite foreign to the localities in 

 which these materials are found ; for similar rocks do not occur 

 in position anywhere in the Miocene district. Whole mountain- 

 masses and ranges consisting of exactly the same materials, how- 



