i9o6.] SEE— THE CAUSE OF EARTHQUAKES. 329 



§21. Avicenna's views on mountain formation. 



Lyell justly remarks that it is surprising to find among the 

 extant fragments of Avicenna, Arabian physician and astronomer 

 of the tenth century, a treatise on the " Formation and Classification 

 of Minerals," characterized by considerable merit, the second chap- 

 ter of which is '' On the Cause of Mountains." Mountains, accord- 

 ing to Avicenna, are formed, some by essential, others by accidental 

 causes. And in illustration of the essential causes, he cites '' a 

 violent earthquake, by which land is elevated, and becomes a moun- 

 tain." In regard to the accidental causes he mentions excavation 

 by water or erosion, which produces cavities, such that adjoining 

 land is made to stand out and form eminences. 



The theory of mountain formation adopted in this paper was 

 therefore foreshadowed by Avicenna in the tenth century of our era. 

 It is extremely remarkable that so simple , an explanation should 

 have been allowed to slumber for so many centuries, while artificial 

 and highly unsatisfactory hypotheses were in use. 



V. Explanation of the Elevation of Particular Mountain 



Ranges and Plateaus. 



§ 22. On the uplifting of the Andes. 



We have already seen that the Andes have been uplifted by the 

 injection of lava beneath the crust in the earthquakes incident to 

 the heaving of the Andean Valley in the adjacent sea. This has 

 been the chief cause of the original uplift of these great mountains, 

 and the resulting explanation suffices to account for all the principal 

 phenomena. Thus we explain the gentle slope of the mountains 



and Martin, who show that the coast was elevated for more than a hundred 

 miles, though slight depressions also occurred in a few places. Elevations of 7 

 to 20 feet were common, and so little change had occurred in 1905 that Tarr 

 and Martin were able to illustrate their memoir by photographs of the most 

 convincing character. The barnacles and other marine animals were still 

 adhering to the rocks, and there could be no possible doubt about the fact 

 of the elevation. The depression of some areas was made equally clear by 

 the encroachment of the salt water upon forests, which were thus killed. Two 

 of the shocks at this great earthquake (September 10-15) were particularly 

 terrible, the motions recorded in Tokio, 3,300 miles away, being ^ and Y% 

 inch respectively. Note added December 3, 1906. 



