﻿158 PEOP. T. G. BONNET ON ANTIGOEITE [MaV I908, 



crystalline rocks, including that called griiner schiefer by the 

 Swiss geologists. I have examined under the microscope a specimen 

 of serpentine from the Val Bognanco, and another from the shoal 

 near the left bank of the Tosa, which might possibly have come 

 from the Yal Devero, but more probably from the Yal Yigezzo, 

 selecting the one to represent a moderately schistose variety, and the 

 other one of the most schistose. The former rock is of a rather 

 light greenish-grey colour, with small dark mottling. Under the 

 microscope it is seen to consist of matted antigorite, the flakes 

 seldom, if ever, exceeding -007 inch, and showing sometimes ' thorn- 

 structure,' sometimes a slight parallelism. The only trace of augite 

 consists of ' cloudlets ' of minute granules, seeming, with ordinary 

 light, like a dust, only a very few of which show a fairly bright- 

 yellow tint with crossing nicols. The iron-oxide is much as is 

 described above. The other specimen, rather conspicuously schistose, 

 is of a grej-ish-green colour, slightly mottled with dark ; under the 

 microscope it is seen to consist of antigorite, with a little residual 

 augite in aggregated granules, which often have a more flaky 

 aspect and lower polarization-tints than is usual (perhaps from 

 incipient decomposition), and with magnetite, both obviously 

 crushed. The antigorite is small, seldom, if ever, exceeding 

 •004 inch, and shows a foliated structure, though not quite so 

 conspicuously as I had expected. Enough to say that these 

 serpentines of the Tosa valley, in both megascopic and micro- 

 scopic aspect, so closely resemble those with which I was already 

 familiar in the Yispthal, that I could not distinguish them, if 

 without labels. 



We see then that antigorite-serpentine, probably derived from an 

 augite-olivine rock, is abundant in the region west of the Tosa 

 from Poppiano to Domo d'Ossola, and is found in the Yal Yigezzo,^ 

 but its occurrence in situ in the Yal Antigorio itself is very doubtful. 

 Thus the original specimen may have been obtained, either from 

 an erratic in the lower part of that valley, or from an actual outcrop 

 in a tributary one (such as the Yal Devero or the Yal Bognanco), 

 to which the name of the main valley has been rather inaccurately 

 attached. The proof of its absence from the Yal Antigorio is 

 obviously not complete, but could only be made so by long and 

 laborious work, for which I have now neither the strength nor the 

 inclination, and I am content to leave the task to members of the 

 Italian Geological Survey. 



II. Othee Antigoeite-Serpentines. 



Since the publication in November 1905 of the paper by Miss Eaisin 

 and myself, I have obtained some more information on antigorite. 

 About a year ago. Dr. J. M. Bell, Director of the New Zealand 



^ Here, according to Dr. Trarerso (' Geologia dell' Ossola' 1895, pp. 166- 

 169), peridotites also occur. 



