REPORT ON AN INVESTIGATION OF THE GEOLOGICAL 

 STRUCTURE OF THE ALPS.' 



By bailey WILLIS 



Eight years ago I first had the pleasure of meeting Prof. Maurice 

 Lugeon on the memorable occasion of his striking address and remark- 

 able triumph at the Vienna Congress of Geologists in 1903. The sub- 

 ject of overthrusts which he then discussed so graphically and with 

 so much force was not unfamiliar to me, that type of structure having 

 been recognized first by the American geologist Rogers, whose obser- 

 vations I had had occasion to verify. I was, therefore, fully prepared 

 to accept the view that the Alps had been overthrust. I did not then, 

 and I do not now, doubt that they consist chiefly of overthrust masses. 

 Nor do I question the amount of displacement. Even the greatest 

 horizontal movements which are postulated to account for the various 

 nappes that have been observed, are relatively small as compared 

 with the long arcs of the earth's periphery, in which the movement 

 must have originated; and the accumulated effect which we may 

 observe in any case should not occasion doubt. 



It is a pleasure to me to be able to agree with Prof. Lugeon in these 

 fundamental conceptions of the importance and extent of overthrust- 

 ing in the structure of mountain chains, and particularly of the Alps. 

 I regret the more that there are differences of opinion between us as 

 to the mechanics of overthrusts, and that this divergence of interpre- 

 tation is such that I have not been able to accept his views on the 

 structure of the Alps as cordially and fully as I should like to do. 

 But, inasmuch as Alpine structure is one of the great types from which 

 our science draws essential conclusions, I hold it to be important to 

 reach a correct interpretation of it, and I have for some years assidu- 

 ously endeavored to understand the basis of Prof. Lugeon's 

 views and the grounds upon which they have been accepted generally 

 by European geologists. Through the aid of the Smithsonian Insti- 



^ This investigation was carried on by means of a grant from the Smith- 

 sonian Institution in 1907- 



Smithsonian Miscellaneous Collections, Vol. 56, No. 31 



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