1884.] on the Building of the Alps. 67 



extent, largely composed of crystalline rocks, and that with this 

 geological age commenced a long continuous period of depression, 

 lasting into Tertiary times ; (4) that a land surface of considerable 

 extent existed at a yet earlier period, and that this in the Carbo- 

 niferous age was watered by streams and clothed with vegetation — 

 whether there were mountains then it is impossible to say, but the 

 evidence certainly points to the conclusion that the ground was hilly ; 

 (5) that anterior to the last-named period there is a great gap in our 

 records ; the older rocks, whose stratigraphical position can be ascer- 

 tained, being much metamorphosed, so that we appear justified in con- 

 cluding that all the more important mineral changes which they had 

 undergone occurred in pre-Carboniferous times — namely, that the later 

 Pala3ozoic land surfaces consisted of gneiss and schists in all important 

 respects identical with those which now exist. 



I have thus led you step by step — by processes, I trust, of cautious 

 induction — to the result that the Alps, as an irregular land surface, 

 are a very ancient feature in the contour of the earth, and that the 

 gneisses and crystalline schists, whereof they so largely consist, are 

 rocks of very great antiquity. Let us now attempt to advance a 

 step further by attacking the problem from another side. Hitherto 

 we have been working downwards from the newer to the older, from 

 the rocks of known towards those of unknown date. Beginning 

 now in the unknown, beginning with the most remote that we can 

 find, let us proceed onwards toward the more recent and more 

 recognisable. 



This is a task of no slight difficulty. The ordinary rules of strati- 

 graphical inference frequently fail us ; nay, if blindly followed, would 

 lead us to the most erroneous conclusions. In the apparent succes- 

 sion of strata in a mountain range the last may be first and the first 

 last in the literal sense of the words. Beds may be repeated again and 

 again by great folds, now in the direct, now in the inverse order of their 

 superposition. They may have been faulted and then folded, or 

 folded and then faulted, and the difficulty is augmented by the vast 

 scale on which these earth movements have taken place, by the frequent 

 impossibility of scaling the crags or pinnacles where critical sections 

 are disclosed, and by the masking of large areas of surface by snow and 

 glacier, or by debris and vegetation. Yet more, the consciousness of 

 these difficulties produces in the mind — I speak for myself — a sort of 

 hesitation and scepticism, which are most unfavourable for inductive 

 reasoning. Knowing not what features are of importance, one is per- 

 plexed by the variety of facts that seem to call for notice ; knowing 

 how easily one may be deceived, one hesitates to draw conclusions. I 

 am often painfully conscious of how much I have lost in a previous 

 journey from not having remarked some fact to which a fortunate 

 accident has just compelled my attention. In this part, therefore, I 

 must be pardoned if I speak with considerable hesitation and do not 

 attempt more than to state those inferences which seem to me 

 warranted by facts. 



