204 Prof. T. G. Bonney—Quartz-Schists from the Alps. 
IIJ.—On Some Quvarrz-scHists FROM THE ALPS. 
By Prof. T. G. Bonney, D.Se., LL.D., F.R.S., F.G.S. 
THICK mass of bedded schists, as I have described in more 
than one paper,’ occupies the highest position among the so- 
called metamorphic rocks of the Alps. With the exception of some 
eneisses—so far as I know of a porphyritic character, and almost 
certainly intrusive granites modified by pressure—and various green 
schists, which, in part at least, are basic igneous rocks, similarly 
affected,” the group, which may be traced from one end of the chain 
to the other, consists of altered sediments. Calcareous mica-schists 
are its most abundant members. The commonest types are dark 
schists varying from lead colour to black (the Thon-schiefer or Thon- 
glimmer-schiefer of many Continental authors) from which the calcite 
sometimes disappears, and greyish schists in which there is not 
‘much mica (the kalkhaltig glimmer-schiefer of the same, which locally 
becomes a white marble*). Quartz-schists also occur, sometimes 
merely as lamine alternating with the darker mica-schists—like sand 
and clay in certain stratified rocks—sometimes in beds. These, so far 
as I know, are of moderate thickness and white in colour. 
That the various schists are associated exactly as are shales, lime- - 
stones, and sands in ordinary stratified masses cannot, I think, be 
doubted.* The persistence of lithological types over large areas 
is often remarkable ; even the peculiar black mica-schist with dark 
-garnets can be traced, to my knowledge, for more than thirty miles 
along the general strike of the group.’ Still changes occur, especially 
in the transverse direction. The group of dark-coloured mica-schist, 
-of which the above-named garnet-bearing rock is a member, occupies 
-a broad strip for some miles H.N.E of Monte Leone, but for a con- 
‘siderable distance west of that mountain the rocks become lighter in 
colour, and the darker type is restricted to the northern margin. 
We perceive the change if we ascend towards the Simplon Pass 
from the Rhone Valley ; it is even more marked, if we extend our 
examination up the Vispthal as far as the outlying masses of the 
‘same group near the range of Monte Rosa. 
The quartz-schists, so far as I know, are not always present 
and are generally of subordinate importance. But they occur at 
intervals over a considerable part of the chain. My collection 
contains specimens from the neighbourhood of Windisch Matrey 
(i.e. very near the Gross Glockner) to the district of the Great St. 
Bernard.® But I purpose to restrict my description mainly to the 
quartz-schists which occur in the neighbourhood of Saas-Fee, since 
here I have studied them in more detail. In this neighbourhood 
1 Q.J.G.S. vol. xlii. (Presid. Address) xlv. p. 67; vol. xlvi. p. 187. 
2 Q.J.G.8. vol. xlix. p. 94. 3 Sometimes dolomitic. 
4 I have examined them more or less minutely, over various Alpine regions, from 
e Viso to the Gross-Glockner. 
5 Q.J.G.S. vol. xlvi. p. 199, ete. 
5 T have not been east of the former among the crystalline schists, nor found them 
west of the latter in any journey made since I began to pay minute attention to the 
_ Alpine schists. 
Q. 
Q. 
th 
