Vol. 50.] MESOZOIC EOCKS, EXC. IN THE LEPONTINE ALPS. 28 5 



19. Mesozoic Rocks and Crystalline Schists in the Lepontine Alps. 

 By T. G. Bonnet, D.Sc, LL.D., F.R.S., F.G.S., Professor of 

 Geology in University College, London, and Fellow of St. John's 

 College, Cambridge. (Bead April 11th, 1894.) 



Contents. p 



I. Introduction 285 



IT. The Altkirche Marble 287 



III. The Val Canaria Section 297 



IV. Section South of the Val Bedretto 299 



V. General Conclusions , . . 301 



I. Introduction. 



My communication to the Society ' On the Crystalline Schists of 

 the Lepontine Alps " has elicited a paper from Dr. F. M. Stapff," 

 and has been noticed at some length by Prof. Heim in a recent 

 publication of the Swiss Geological Survey. 3 The pages of this 

 Journal, for more than one reason, cannot well be used for purposes 

 directly controversial ; so that, as I expect to find before long a more 

 suitable opportunity and place, I content myself at present with 

 remarking generally that Dr. Stapff's main argument is difficult to 

 discuss, because everything turns upon the exact geological position 

 and the microscopic structure of certain specimens, matters in which 

 photographs are of little avail ; and that Prof. Heim, as will be 

 incidentally shown in the course of this paper, really adds nothing 

 to his original argument. That rests, as I stated in my former 

 communication, upon a correlation of certain rocks which I consider 

 highly improbable, and an identification of certain minerals which I 

 affirm without hesitation to be erroneous. 



In that communication I maintained that there was (a) no valid 

 proof, only a prima facie presumption, that the Altkirche 4 marble 

 was of Jurassic age : and (6) not only no proof at all that the Val 

 Piora schists were of this age, but also strong evidence that they 

 were much more ancient. 



On the first issue I claimed a verdict of ' not proven.' In the 

 hope of finding more definite evidence, even if it went against me, I 

 have revisited the district. In 1891 I made a brief examination of 

 the sedimentary rocks near the Furka Pass, in company with Mr. 

 James Eccles, and last summer I spent a week in the upper part of the 

 TJrserenthal. My friend also, in the interval, went over some of the 



1 Quart. Journ. Geol. Soc. vol. xlvi. (1890) p. 187. 



2 Geol. Mag. 1892, p. 6. Since the words above were written a second paper 

 has appeared in the same periodical, 1894, p. 152, to which also the same remark 

 applies. 



* Beitrage zur geol. Karte der Schweiz, Lief. xxv. 1891. 



4 This appears to be a more correct spelling than that used in my former 

 paper. 



Q.J.G.S. No. 199. x 



