360 CLIMATIC CONDITIONS OF THE GLACIAL EPOCH. 



present connection, at some length, because it seemed to furnish a good 

 instance of the propensity of enthusiastic glacialists to exaggerate the limits 

 of the ice masses, not only in the Alps but in other formerly glaciated 

 regions.* 



Extensive observations in every part of the Alps, as well as the examina- 

 tion of much that has been published in regard to the glacial geology of 

 that region, has led the writer to infer that during the period of the greatest 

 development of the glaciers in that range, its eastern portion was less 

 extensively glaciated than the western. This would be in accordance with 

 what we see at the present time, the glaciers of Bavaria and Tyrol being 

 very inferior ia magnitude to those of Switzerland. But the geological 

 observer cannot fill to be imj^ressed with the proofs ever3\vhere furnished in 

 the Eastern Alps of the former much greater volume of the streams occupy- 

 ing the valleys. 



The question of the position of the line indicating the extreme limits 

 reached by the grand glacier which found its way down the valley of the 

 Rhone is also one not entirely settled. That, in general, the Jura acted as a 

 barrier to its farther progress, and that this range was invaded by the ice 

 to but a slight extent, is clearly shown by the position of the morainic debris 

 along its southeastern slopes. Following down the river Rhone, according 

 to the minute and laborious investigations of Messrs. Falsan and Chantre,t 

 the ice How made its way for a distance of 400 kilometers (285 miles) from 

 its head on the flanks of the Galenstock, combining with many smaller 

 glaciers coming down the valleys on tlie northwestern slope of the Dauphiny 

 Alps, and ending on the hills near Lyons, opposite the mass of Mont d'Or, 

 and on the plateau of the Dombes. The thickness of the ice is thought to 

 have been from 1,200 to 1,680 meters in its upper portion; at its lower end 

 it had thinned down to less than fifty. 



* Zittel adduces as an argument in favor f)f the glacial origin of the supposed morainic matter in the region 

 described above, that there are boulders found in it which could hardly have reached their present position with- 

 out the aid of ice. He admits, however, that similar difficulties present themselves in connection with the older 

 "diluvium," wliich he himself does not believe to be of glacial origin, and of which he remarks "that the presence 

 in it of large quantities of rolled fragments of crystalline rocks belonging to the Central Alps presents a iiroblem 

 which has not yet been snti.sfactorily solved." The present writer believes that the sohition is not rendered any 

 less difficult by invoking the aid of glaciers. If the presence of boulders in a region where they do not belong can 

 only be accounted for in that way, it will be necessary to extend the ice sheet as far north as Holland, and to admit 

 tliat it advanced botli from the northeast and from the southwest. (See farther on p. 369.) 



t Monographic Geologique des Anciens GlacierG et du Terrain Erratique de la Partie Moyeiine du Bassiu du 

 Rhone, 2 volumes, Lyons, 1880. 



