Vol. 50.] GNEISSES IN THE COTTIAN SEQUENCE. 277 



Mr. Barrow observed that the paper before the Society might be 

 divided into four parts. The first dealt with the evidence of the 

 intrusive nature of the coarse gneiss ; and the Author was to be 

 congratulated on the careful manner in which he had gone over the 

 ground, and the clearness with which he had summarized his 

 evidence. The second referred to the contact-effects of the intrusion. 

 But here the evidence was too vague to enable us to form any 

 opinion as to the accuracy of the Author's views. Did he suppose 

 that the crystalline character of the surrounding schists and gneisses 

 was essentially due to this intrusion or mereby modified by it? 

 Thirdly, the evidence of age would require most searching examina- 

 tion. The movements on the margins of mountains have frequently 

 associated fossil-bearing rocks with older crystalline schists in such 

 a manner as to have deceived some of our most acute observers, 

 and led to the conclusion that they were all of one age. Lastly, 

 the fact that the great earth-movements do not appear to have 

 effected any crushing in the coarsely crystalline rocks was not a 

 satisfactory line of argument as to the age of the rocks. Powerful 

 earth-movements frequently fail to crush more than the outer 

 margins of crystalline areas ; these harder rocks escaping at the 

 expense of the softer and often unaltered sediments by which they 

 are flanked. The latter, indeed, are frequently themselves altered 

 to finely schistose rocks giving every appearance of a passage from 

 one series to the other. 



Prof. Eonney said that he had only examined these Cottian 

 gneisses in one locality, and had found it extremely difficult to 

 make out what their origin might be. If fluxion-gneisses, which 

 was very possible, they were rather peculiar. He quite agreed 

 that a group of granitic rocks existed in the Alps later than 

 any of the crystalline schists, but that did not prove that they 

 were Tertiary, Secondary," or Palaeozoic. The discovery of radio- 

 laria in the ' scbistes lustres ' did not show that these were Palaeo- 

 zoic, because, if the rocks were schists, there would be no radiolaria 

 remaining ; and nothing was commoner in the Alps than to find 

 wedges of Jurassic, or Triassic, or older but comparatively unaltered 

 sediments in the crystalline masses. Also the Carboniferous rock was 

 very apt to have its base full of material from the older underlying 

 rock. As to the age of the gneiss, he agreed with Mr. Barrow that 

 no great value attached to the fact of these rocks being uncrushed. 

 He gave instances, and said he felt incredulous as to a Pliocene 

 age, because there was no evidence, so far as he knew, of outbreaks 

 of igneous rock of Tertiary age, except the basalts in the S.E. The 

 Permian or some part of the Trias seemed the latest possible. 



Mr. A. M. Davies said that he had accompanied Dr. Gregory on 

 his last visit to the Cottians, and had seen the greater part of the 

 evidence on which his conclusions were based. Some of the junc- 

 tions (such as that at the Eoc del Pelvo) showed striking evidences 

 of intrusion, but there was room for much more detailed study ; 

 and the mountainous nature of the district would add greatly to the 



