Prof. T. G. Bonney—Serpentines from the Rhetian Alps. 541 
sists of a felspar—generally so much kaolinized, or replaced by 
secondary microlithic minerals, as to have lost its characteristic 
aspect, and to be a kind of “saussurite,” but here and there retaining 
traces of plagioclastic twinning—and of fairly well preserved diallage. 
The felspathic constituent has the granular outline common in 
gabbro, and has probably been labradorite. A crack is filled with a 
chloritie mineral. The pyroxenic constituent of the finer variety is 
augite, and there are grains of a fibrous serpentinous mineral, which 
also fills cracks and appears to be disseminated in the slide. 
Rather higher up the valley, on the right bank of a grassy basin, 
near some chalets (Stalvedro), is a small excavation in a band of 
hard crystalline limestone beneath a shivery mica schist, on the 
eastern side of which is a shattered serpentine underlying a greenish 
schist, its mode of occurrence suggesting intrusion. The limestone 
under the microscope appears to be more strictly a dolomite, with 
minute quartz grains (of secondary origin) interspersed, in parts rather 
thickly, and traversed by cracks filled with the latter mineral. Above 
this spot there is no more serpentine on the Julier pass, but two 
patches are laid down on the ascent to the Septimer, which diverges 
at Bivio Stella. 
Following roughly the directions indicated by the above sporadic 
exposures—towards the S.H.—we find another mass of serpentine on 
the northern side of the Maloya Pass. It forms a headland on the 
left bank of the Silser See, and extends for some distance up the 
mountain side. This rock agrees generally in colour with the last 
named, but is less crushed than is usual with the others, and exhibits 
the brown weathering, massive structure, and sharp, rather irregular 
jointing so characteristic of true serpentines. Microscopically it has 
a general resemblance to the rock from above Marmels, as it con- 
tains both enstatite and augite. The former is much altered, the 
latter (of irregular outline) in fair preservation ; one grain appears 
to be diallage ; most of the others resemble normal augite; none of 
the olivine has escaped quite unaltered, but in parts of the slide the 
change seems less complete than is the case in the other serpentines. 
In this slide also are visible some of the black grains described above. 
The last two serpentines then may be roughly classed as altered 
lherzolites ; and all are altered peridotites. 
A considerable number of patches of serpentine appear on Von 
Hauer’s map about the head of the Schalfik-Thal and Landquart-Thal. 
From them probably were derived several pebbles which I saw near 
Chur; these corresponded in general appearance with the specimens 
already described. 
It is impossible to offer an opinion as to the geologic age of these 
peridotites. From their shattered condition it is in the highest 
degree probable that they have partaken of some, if not all of the great 
movements which have affected the Alps, and so are at least older 
than the Middle Tertiary period. They are mapped as intrusive in 
Bundner Schiefer, which, according to Von Hauer and Theobald, 
belong to the Lower Lias. The latter, however, considers some of 
the schist near Molins to be of much earlier date, and I confess I 
