1028 REPORT—1885. 
a district can only be worked out by the exercise of patient and cautious induction 
from observations extended over a wide area. 
2, The non-crystalline rocks of the Alps are of various ages. There are some 
of Carboniferous age, but the great period of continuous deposition generally begins 
with some part of the Trias. The conglomerates, which often occur at the base of 
the non-crystalline deposits, indicate that the principal metamorphism of the erys- 
talline series was anterior to both these epochs. There is at present no reason to 
suppose that either in the Central Alps or for some distance on each side there 
are any representatives of the earlier Paleozoics. I believe that the conglomerates 
at the base of the Carboniferous contain fragments of the later crystalline rocks of 
the Alps as well as of some of the earlier—though I do not assert that these crys- 
talline rocks have undergone no modifications since Carboniferous times. 
3. In the heart of the principal Alpine chains, and apparently at the base of 
everything, are coarsely crystalline gneisses. These differ little from granites, 
except that they generally—almost always—exhibit a certain foliation, and 
occasionally seem to be interbedded with thin seams of micaceous schists or flagg 
fine-grained beds, 
4, On examining these latter we find reason to believe that they are generally due 
to crushing. Their strike agrees with that of the apparent foliation in these older 
rocks, and with that of a foliation which is also present in the newer crystalline 
rocks, This corresponds with the strike of the main physical features of the dis- 
trict, and with the cleavage in the included troughs of sedimentary rock. It runs 
for great distances with remarkable uniformity, e.g., from the Maderanerthal to 
the upper part of the Lukmanier Pass the strike of this foliation does not materially 
vary from W.S.W.-E.N.E. 
5. This apparent foliation is due to the development of extremely thin films of 
@ micaceous mineral, In many cases it causes the rock to bear the aspect of a 
highly micaceous schist; yet, on examining a transverse section, it is seen dis- 
tinctly tobe a crushed gneiss; 7.e., though so conspicuous, it isa mere varnish. As 
it thus differs materially from a true foliation, it would be convenient to give ita 
name, and I should propose to call it the ‘sheen surface” It is, in fact, a kind of 
‘cleavage foliation,’ that is, a foliation due to cleavage, and subsequent to it. But 
though from certain points of view so conspicucus, its minerals often constitute a 
very small part of the mass of the rock. 
6. The pressure which has produced this ‘sheen surface’ has in many cases 
affected the orientation of the minerals, which are present in the true ‘ foliation’ 
layers of the more distinctly foliated, 7.e., mineral-banded, rocks. It has affected 
these minerals as pressure affects the constituents of a sedimentary rock. 
7. In the crystalline schists yery commonly the ‘sheen surface’ corresponds with 
the original foliation surface, as in the slates the cleavage sometimes does with the 
bedding. This is due to the fact that the axes of the great folds often make a very 
high angle with the horizon. It may, however (like a cleavage surface), be seen 
crossing the foliation at all angles. 
8. Thus a non-foliated crystalline rock may be rendered to some extent foliated 
by pressure (followed by a certain amount of mineralisation) ; z.e., some gneisses 
may be formed by crushing from granites, some schists out of other igneous rocks. 
It may obliterate an earlier foliation, or it may intensify it, or it may produce an 
independent and more fissile foliation. 
In this sense gneiss may he said to pass into granite, because a rock which is 
now, both macroscopically and microscopically, a gneiss may prove to be a granite 
which has in some parts yielded to pressure more than in others. 
9. As we pass outwards from the great central granitoid masses we come to 
gneisses and schists where the evidence of some kind of stratification becomes more 
marked ; bands of crystalline limestone, quartzite and granulite being associated 
with mica schist of many kinds—simple, garnetiferous, staurolitic, actinolitic, and 
the like—the bands of different mineral character and composition varying from 
mere streaks to layers which are many yards in thickness. In fact, the above-named 
rocks are associated exactly as limestones, sandstones, and clays are associated in 
the ordinary sedimentaries, 
