54 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



followed in less tilted positions. More striking than this scheme 

 of Alpine structure is De Saussure's admirable description of 

 the fan-shaped arrangement of the schists in the Central Alps 

 of western Switzerland, and his proof that the longitudinal 

 valleys and the chains of secondary rock follow the strike of 

 the strata and the continuation of the main ridge, remaining 

 parallel with the leading or central chain. Saussure further set 

 forth the asymmetry of form presented by the Western Alps, in 

 respect of their gradual descent to the Swiss plains on the north 

 side of the Alps, and their abrupt descent on the Italian side, 

 He examined the mineral composition of the rocks, and the 

 alternation, succession, and position of the different kinds of 

 rock. He also studied the topographical, meteorological, and 

 physical relations in the mountains. A permanent addition to 

 the facts of physical geography was made by his height measure- 

 ments, his observations of electrical atmospheric disturbances, 

 his determinations of' the snow-line, rise of temperature in 

 the ground and in the depths of the lakes, his investiga- 

 tions of glaciers, and of the distribution of plants at different 

 altitudes. 



It was not until after the publication of the first two volumes 

 of his work that De Saussure became acquainted with Werner's 

 geognostic and mineralogical writings. He welcomed the new 

 methods and additional knowledge supplied by Werner, and 

 promptly tried to apply them in the district he was himself 

 examining. Hence we cannot blame De Saussure when we 

 find in the third and fourth volumes of his work, certain 

 ideas about rock structure and mountain upheaval that appear 

 contradictory to views expressed in the earlier volumes. 



De Saussure also changed his opinions more than once 

 about valley-erosion and about the origin of the immense 

 thicknesses of debris and pebble deposits in the Rhone Valley 

 and at the foot of the Alps. Like Professor Arduino of 

 Padua, De Saussure was intensely interested in the nagelflue 

 conglomerates and morainic accumulations and erratic blocks 

 on the outer Alpine slopes, but was no more successful than 

 Arduino in arriving at an explanation. He referred them all 

 to one geological period, during which he thought gigantic 

 inthrows of the crust had taken place, and the waters of the 

 ocean rushing into the crust-basins had fragmented, torn away, 

 and scattered large masses of rock. 



With our present intimate knowledge of glaciation, it seems 



