1906.] 



SEE— THE CAUSE OF EARTHQUAKES. 333 



down. Here is a land drenched in rain and reeking with mists, where the 

 bright sun is a surprise and a joy in spite of his heat. In these dense forests, 

 with their twisting vines and hanging lianas, a man without a path can 

 force his way with difficulty a mile a day. ..." 



'From these accounts, and from the greater steepness of the 

 eastern side of the Andes, I think it clear that the perpetual rain 

 which falls there sinks down as if the country were overlaid by a 

 deep sea, and thus in effect the Andes are on a narrow strip between 

 two oceans. Hence the terrific effects of the volcanic forces, which 

 have not only upraised the peaks and chains, but also plateaus like 

 that of Titacaca. While the western ocean furnished the forces 

 for the original uplift of the chain, the reeking tropical rains must 

 have augmented these forces in the later stages of the Andean de- 

 velopment, and this amply accounts for the activity of the volcanoes 

 in the eastern range. These volcanoes might, it is true, be accounted 

 for by the leakage of the ocean, yet it seems probable that the 

 enormous surface rainfall can hardly fail to increase the volcanic 

 violence where the range is already formed, and the rocks broken 

 and tilted to permit of a maximum seepage of the ceaseless tropical 

 rains which constantly soak the eastern side of the mountains. 

 § 23. On the process involved in the elevation of the Alps. 

 In the "Face of the Earth," Vol. II, p. 121, Professor Suess 

 shows that " the prevailing tangential movement in the Alps and 

 Pyrenees " is towards the north. Thus we see that the plains of 

 Lombardy and the Valley of the Po constituted the sea valley which 

 was most active in exerting the northern tangential thrusts in fold- 

 ing the Swass Alps. Professor Suess (Vol. I, p. 274) remarks on 

 the similarity of the Swabian-Franconian sunken area north of the 

 Alps, and the depression of the Adriatic to the south. An exami- 

 nation of almost any good map will convince anyone that the 

 Adriatic once covered the \yhole of the valley of the Po. The 

 maps given by Reclus in his large work " La Terre," p. 184, show 

 the jutting spurs radiating from the plains of Lombardy into the 

 surrounding mountains on all sides. This result, therefore, is a very 

 happy confirmation of the theory. It is also satisfactory to find 

 that the Pennine range of the Alps, nearest the valley of the Po, 

 including ]\It. Blanc, is the highest of these great mountains. The 

 highest range of the Himalayas, including Mt. Everest, also stands 



