Vol. 50.] GNEISSES IN THE COTTIAN SEQUENCE. 269 



reddish siliceous schists on the south side of Monte Cruzeau, and close 

 beside the great mass of serpentine cut through by the road from 

 Fenestrelle to Cesana. The point at which the beds occur is on a 

 line between the great mass of Triassic limestone that forms the Gran 

 Roc and Roc del Boucher, with some smaller exposures of the same 

 rocks marked by Vasseur and Carez north of Monte Cruzeau. It 

 seemed probable, therefore, that the fossiliferous phthanite might 

 be really a member of the Trias series folded in with or faulted 

 down into the schists. Prof. Parona does not consider this hypothesis 

 in his paper, and I therefore thought it advisable to examine the 

 area independently. Before doing this, however, I examined part 

 of the Roc del Boucher limestone and its basal graphitic beds, and 

 worked three times over the Triassic series of Chaberton ; but in 

 neither could I find any trace of the phthanite. Nor is there any 

 evidence that would suggest an infold of the Trias in the schists at 

 this point. Moreover, in working along the Fenestrelle road from 

 Cesana, a few thin bands of a similar phthanite and siliceous schists 

 are found to occur interbedded in extremely typical calc-schists. 



[Dr. Brugnatelli has announced his intention of describing fully 

 the stratigraphical relations of the phthanites (Parona, op. cit. 

 p. 306). I did not therefore attempt to trace the beds to the north, 

 and prefer to leave any further description till after Dr. Brugna- 

 telli's memoir has appeared. I must apologize to him for having 

 possibly to some extent anticipated his conclusions, but it appeared 

 absolutely necessary to insert these remarks in the discussion of the 

 age of the schists.] 



I was consequently compelled to abandon the hypothesis which I 

 went to Cesana expecting to be able to prove, and can see no escape 

 from the conclusion that the radiolaria are of the same age as the 

 calc-schists. 



It is somewhat unfortunate that the only fossils found, or which are 

 likely to be found, are radiolaria, because their evidence as to the 

 age of the deposits in which they occur is very unsatisfactory. The 

 radiolaria are also in a very imperfect condition of preservation, but 

 no doubts as to their authenticity can be entertained, as Prof. 

 Nicholson and Dr. Hinde both express themselves quite satisfied 

 with the evidence of the slides prepared from the material which I 

 collected. Dr. Rust, who has examined slides lent by Prof. Parona, 

 not only identifies the fossils as radiolaria, but suggests that they 

 are possibly Tithonian in age ; the stratigraphical evidence is, how- 

 ever, conclusive against the latter opinion. 1 



Prof. Parona has figured a good number of the radiolaria, and 

 has been able to determine the presence of 21 genera and even to 

 identify 7 species. It is probable that better indications as to the age 

 of a radiolarian fauna will always be obtained by the comparison of 

 lists of genera than of species ; more reliance must be placed on the 

 general facies of faunas than on the number of species common to 



1 Psr.na, op. cit. p. 316. 



