198 The Scottish Naturalist. 



system within which they occur, but have without doubt been 

 derived from the higher Alps of Switzerland and Savoy. And 

 the course followed by these foreign erratics has crossed at all 

 angles that which the local glaciers have certainly pursued — 

 occasionally, indeed, the one set of erratics has travelled in a 

 direction exactly opposed to the trend taken by the others. As 

 examples, I may cite the case of the erratics which occur in 

 Petit Bugey. In this district we encounter many locally-derived 

 erratics which have come from Mont du Chat to the west of the 

 Lac du Bourget — that is to say, they have travelled in a north- 

 westerly direction. But in the same neighbourhood are found 

 many erratics of Alpine origin which have been carried from 

 north-east to south-west, or at right angles to the course followed 

 by the local erratics. Again, in the valley of the Seran we have 

 evidence in erratics and terminal moraines of a local glacier 

 which flowed south as far as -the Lyons and Geneva Railway, in 

 the neighbourhood of which, a few miles to the west of Culoz, 

 its terminal moraines may be observed. This is the extinct 

 Glacier du Valromey of MM. Falsan and Chantre. Now it is 

 especially worthy of note that in the same valley we have dis- 

 tinct evidence of an ice-flow from south to north — i.e., up the 

 valley. Erratics and morainic materials which are unquestion- 

 ably of Alpine origin have been followed a long way up the 

 valley — for two-thirds of its length at least. Before they could 

 have entered that valley and approached the slopes of Romey, 

 they must have travelled down the valley of the Rhone from the 

 higher Alps of Savoy in a south-west and south direction until 

 they rounded the Montagne du Grand Colombier. It was only 

 after they had rounded this massive mountain-ridge that they 

 could pursue their course up the valley of the Seran, in a direc- 

 tion precisely opposite to that which they had previously fol- 

 lowed. These and many similar and even more remarkable 

 examples of the " intercrossings " of streams of erratics are 

 described by MM. Falsan and Chantre, and graphically por- 

 trayed in their beautiful and instructive work on the 'Ancient 

 Glaciers and Erratic Deposits of the Basin of the Rhone ; ' and 

 the explanation of the phenomena given by them is extremely 

 simple and convincing. The local erratics and moraines per- 

 tain partly to the commencement and partly to the closing stage 

 of the Glacial Period. Long before the south branch of the 

 great glacier of the Rhone had united with the glacier of the 

 Arve, and this last with the glaciers of Annecy and Beaufurt, 



