﻿156 PROF. T. G. EONNEY OIs^ AKTIGOKITE [^-taV I908, 



visible)/ As at least a dozen were scattered over the few yards 



from which the surface-soil had been partly removed, and two or 



three of them were almost in contact, I infer that a fair number 



must be concealed by the vegetation. The blocks were angular or 



subangular in form, varying in diameter up to about half-a-yard, 



and the rock very closely resembled much of that in the Saasthal, 



being of a fairly dark-green colour, slightly mottled with blacker 



spots, so tough and hard that satisfactory specimens were difficult 



to obtain. It was but slightly schistose, developing under the 



hammer an irregular jointing. Under the microscope the rock is 



found to consist of antigorite, a residual augite, and an iron-oxide. 



The first needs little more than mention, as it resembles much of 



that described in our paper of 1905 : it is practically colourless and 



non-pleochroic in a thin slice ; it occurs in flakes, with hardly an 



approach to orientation and rather variable in size, the largest 



being about -025 inch in length, but most of them not exceeding 



the half of this. The augite, forming about one-eighth of the 



rock, occurs in irregular grains or granules, often with a slightly 



' dusty ' aspect, the former sometimes giving, for a space of about 



a fiftieth of an inch, fairly uniform polarization-tints, sometimes 



broken up, perhaps by pressure, into differently-coloured granules. 



The mineral is in process of conversion into antigorite, for it 



includes or is pierced by flakes of the latter, which bear no relation 



to the cleavage- planes in the few cases where these can be detected. 



The iron-oxide occurs in sporadic granules and irregularly-outlined 



grains, occasionally pierced by small flakes of antigorite. Examined 



by reflected light they have a general resemblance to magnetite, 



but the lustre seems to me not quite so bright as is usual ; so 



possibly they are chromite or ilmenite. 



Evidently these blocks are relics of the glacier which formerly 

 descended the Yal Devero — part of a scattered lateral moraine on 

 its right bank. At the head of this valley the map records an 

 outcrop of serpentine, measuring about 2500 yards from east to 

 west, and 1500 yards from north to south, the apparent thick- 

 ness of which is said to be 'several hundred feet'.^ This is 

 crossed by the Geisspfad Pass (8365 feet) from Binn to Baceno. 

 Some years ago my friend Mr. J. Eccles, E.G.S., kindly gave me 

 two specimens of this rock. These consist mainly of an acicular 

 green hornblende embedded in talc. But as the former mineral 

 indicates pressure-metamorphism,^ and a schistose serpentine may 

 be altered into a talc-schist,* and as they were obtained near the 

 junction with gneiss on the Swiss side, they are probably abnormal ; 

 for according to Dr. Preiswerk's account of the mass, to which I shall 

 again refer, the bulk of it, which on the Italian side breaks up into 

 separate sill-like intrusions, must often resemble the above-described 



^ The place was nearly opposite the actual junction of the Devero torrent 

 with the Tosa and at least 100 feet (I forgot to take a note) above it. 



2 John Ball, ' Central Alps ' p. 254 (ed. 1866). 



3 Quart. Journ. Geol. Soc. vol. xlix (1895) p. 94. 



4 Geol. Mag. dec. iii, vol. vii (1890) p. 540. 



