ON THE VARIOLITIC EOCKS OF MONT GENEVEE. 



305 



thus shown to be due to great aggregations of chloritic decompo- 

 sition-products. Other patches in the neighbourhood are true 

 serpentines formed from olivine, and contain areas of felspar, dial- 

 lage, and bronzite. The structure exactly resembles that of the 

 ordinary serpentines of the Cottians, one of which is well shown a 

 little over two kilometres to the north-east, at the upper angle in 



Eig. 2. — The Col du Chenaillet, from the north. 



B.S. Brecciated serpentine. S. Serpentine. 



V. Variolite-diabase and Variolite-tiiflf. 



X. Point where fragments of limestone occur in the brecciated serpentine. 



the zigzag on the road between Clavieres and Cesana Torinese. 

 This rock was described last year by Prof. Bonney * as a schistified 

 serpentine. Macroscopically it is almost identical with some from 

 the variolitic area ; under the microscope it is seen to consist of a 

 light green serpentine with a well-marked '• ^Easchenstructur " and 

 areas of altered diallage ; secondary magnetite, either in the form of 

 crystals or dust, and actinolite are both abundant, and the rock is 

 traversed by a comj^lex of chrysotile-veius. 



We have thus to deal with a pseudo-serpentine formed from 

 segregation-masses of diallage and a true serpentine with bronzite. 

 In the case of the former, the junction with the gabbro is so irre- 

 gular that the rock certainly does not result from the intrusion of 

 a dyke richer in pyroxene than the surrounding gabbro. That the 

 true serpentine was not formed from pyroxene seems clear, as it 



* Bonney, "Notes on two Traverses of tlie Crystalline Rocks of the Alps/' 

 Quart. Journ. Geol. Soc. vol. xlv. (188<.)), p. 80. 



