Vol. 63.] ATTKIBUTED TO THE SAVOY AND SWISS ALPS. 305 



But it may be said that I am not dealing quite fairly with 

 Prof. Lugeon's hypothesis, because he does not explicitly claim a 

 transport of more than 90 kilometres (about 56 miles), and this for 

 the Prealpes medianes, so that he may consider the Prealpes 

 exterieures to be thrust forward by the pressure of the others. 

 Still, the whole area disturbed, directly or indirectly, measures 

 fully 80 miles (instead of 75, as I took it). Nevertheless, if my 

 diagrams are considered to be in any way unfair, I should be 

 content to place y about 1| inches nearer BC in fig. 3 (p. 300), and 

 assume the vertical scale in figs. 4 & 5 to be exaggerated in the 

 proportion of 3 : 2 instead of 2 : 1. 



To sum up : in passing judgment on Prof. Lugeon's hypothesis 

 we must remember the following points : — 



(1) That it rests largely, both in his paper and in others of the 

 same general tendency, on correlations of rocks which are taken as 

 axiomatic, although they have been repeatedly disputed on evidence 

 and in papers which it has apparently been found wiser to leave 

 severely alone. 1 



(2) That it receives but little support from Prof. Sollas's 

 experiments, because in them the conditions were so much more 

 favourable to internal movement, both in the arrangement and in 

 the nature of the materials employed. 



(3) That proof is wanting, either of excessive overloading of the 

 Piedmontese lowland in Tertiary times, or of circumstances in the 

 earlier days of the Alps being such as could change rocks from the 

 state of slightly plastic solids to that of viscous fluids. 



(4) That the masses forming the nappes and plis couches 

 must have completed most of their journey, at latest, very early in 

 Pliocene times, because, so soon as continuity was interrupted by the 

 crystalline axis of the Pennines, the vis a tergo would cease. 



The problem of the building of the Alps is both complex and 

 difficult : it is one on which no man can presume to dogmatize; 

 nevertheless I will venture so far as to remark that, while paying 

 due homage to the ingenuity and brilliance of the hypothesis 

 elaborated so skilfully by Prof. Lugeon, and supported by not a few 

 distinguished savants, I still think that the general principles 

 of mountain-building — namely, by crumpling of zones in the 

 earth-crust — advocated by so many geologists from the days of 

 H. D. Rogers onward, modified to some extent by the effects of 

 ■ horsts ' and ' collapses ' as described by Prof. E. Suess, will be found 

 to approach more nearly to the truth. 



[Prof. G. A. J. Cole, when the abstract of this paper appeared, 

 kindly called my attention to a criticism of Prof. Lugeon's views, 



1 It may suffice to enumerate those only for which I can assume respon- 

 sibility r—this Journal, vol. xlv (1889) p. 67 ; vol. xlvi (1890) p. 187 ; vol. xlix 

 (1893) pp. 89, 94, 104; & vol. 1 (1894) pp. 279, 285 (at the end of which is a 

 summary of conclusions). 



Q. J. G. S. No. 251. y 



