RELATION TO MESOZOIC HOCKS IN THE LEPONIINE ALPS. 189 



successive deposition. Great as the modifications resulting from 

 subsequent pressure very frequently are, these may often be separ- 

 ated, and the earlier record, as in the case of a palimpsest, be 

 decyphered. 



In the Alps there exists, as has frequently been pointed out by 

 those who have preceded me *, a great group of crystalline schists, 

 the bulk of which must be metamorphosed sedimentary deposits. 

 This group can be traced, practically without a break, from one 

 end of the chain to the other. These schists certainly overlie, 

 sometimes it would seem unconformably, another great series of 

 gneisses and schists f, generally coarser in texture. These seem to be 

 divisible into two groups differing in lithological characters, of 

 which the upper, though sometimes well developed, is not seldom 

 wanting ; so that instead of the gradual transition from it to the 

 first-named group, which can sometimes be observed, we find the 

 latter resting with marked discordance upon some part of the lower 

 series. The present paper deals mainly with this highest group. 



The oldest unaltered rocks in the Alps generally belong to the 

 lowest part of the Mesozoic system, Jurassic or Triassic (possibly 

 sometimes Permian), but in certain districts not inconsiderable 

 deposits of Carboniferous age (quite disconnected from the last 

 named) occur, and in the North-eastern Alps Palaeozoic rocks of yet 

 earlier date have been identified. All these are practically unaltered. 

 An exceptionally wide experience enables me to affirm without fear 

 of contradiction that, in the case of any large mass which would 

 be referred without hesitation to the Jurassic, Triassic, or Carbon- 

 iferous group, there will not be found, however great may have been 

 the mechanical disturbances which it has undergone, any transition 

 exhibited by it into one of the normal gneisses or schists; at most 

 a raicrofoliation has been developed or a superficial resemblance set 

 up. The crystalline schists also do not exhibit, as a rule, any ten- 

 dency to pass into ordinary sedimentary rocks. Appearances sug- 

 gestive of this transition are found on closer examination to be due 



* I have made no attempt to compile, in accordance with a growing prac- 

 tice, a list of books on Alpine geology, because the greater part of them would 

 have little real beai-ing on the subject of this paper. A list of those treating on 

 the geology of the Lepontine Alps will be found in Von Fritsch's volume, to 

 which and to such as I have used in writing this paper references are given in 

 the text. Others there may be, for I do not pretend to have spent much time 

 in searching ; but if any one has come to conclusions identical with my own, I 

 can assure the author that there is no plagiarism. At the present stage of the 

 questions treated of in this paper, I find work in tlie field or with the micro- 

 scope of far more value than " hours in a library." 



t III the remainder of this paper I follow my invariable practice of using 

 the term schist to express a foliated rock, and so as the equivalent of the " crystal- 

 line schist " of some authors. This is the restriction long ago insisted upon by 

 Jukes. As I have frequently pointed out, the lax use o'l scliisfe and schiefer by 

 continental writers, and of schist by some English geologists, has been a fruitful 

 parent of confusion of thought and inaccuracy of expression. By a foliated rock 

 I me;m one wiiich is crystalline and exhibits a certain parallelisni in its consti- 

 tuent minerals, especially those like mica and hornblende. If in addition to this 

 certain minerals predominate in certain layers, tlie i*ock is also called banded. 

 Thus the terms schist and gneiss imply foliation, but not necessarily banding. 



