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Part IL § vi] CRYSTALLINE ROCKS—SCHISTOSE. 125 
which is the normal type; hornblende-gneiss, where hornblende takes 
the place of mica; cordierite-gneiss, with biotite and blueish cor- 
dierite; protogine-gneiss, where the mica is replaced by tale. 
Like mica-schist, gneiss occurs in vast bedded masses which 
occupy a large space in regions where the older geological formations 
come to the surface. Varieties of it are also found in the meta- 
morphic zone encircling some masses of granite. So coarse is the 
texture of many gneisses that they cannot, in hand-specimens nor 
even in large blocks, be certainly discriminated from granite. In 
such cases it is only by examination in the field and the detection of 
clear evidence of a general foliated structure that their true character 
can be determined. 
An interesting and important rock is met with in some regions of 
gneiss and schist, viz. a schistose conglomerate, in which pebbles 
of quartz and other materials from less than an inch to more than 
a foot in diameter are imbedded ina foliated matrix. Examples of 
this kind are found in the pass of the Téte Noire between Martigny 
and Chamouni, in north-west Ireland, in the islands of Bute, Islay, 
Garvelloch, and different parts of Argyllshire. The pebbles are 
not to be distinguished from the ordinary water-worn blocks of true 
conglomerates; but the original matrix which encloses them has 
been so altered as to acquire a micaceous foliated structure, and to 
wrap the pebbles round as with a kind of glaze. These facts, like 
those already referred to in the microscopic structure of mica-schist, 
are of considerable value in regard to the theory of the origin of 
the crystalline schists. 
Granulite (Leptynite, Eurite schistoide, Weiss-stein)."—A schistose 
ageregate, consisting mainly of orthoclase and quartz, with red 
garnet and some kyanite; is by some petrographers classed as 
an eruptive rock with the granites. It occurs in well-defined 
foliated beds associated with gneiss and other crystalline rocks in 
Saxony, where several varieties of the rock have been observed, 
one of which consists of diallage, triclinic felspar, quartz, garnet, 
and biotite. | 
A few other crystalline rocks, found in comparatively small quan- 
tity, associated with the crystalline schists, may be mentioned here. 
—Garnet-rock, a crystalline-granular aggregate of garnet, horn- 
blende, and magnetite; kyanite-rock, a mixture of blue 
kyanite, red garnet, green smaragdite, and silver-white mica; 
eclogite (omphacite-rock), composed of grass-green smaragdite 
and red garnet; kinzigite, of mica, garnet, and a triclinic felspar. 
Lhe chemical composition of some normal varieties of schistose 
rocks is here appended; but the proportions of the constituents 
vary considerably in different examples of the same rock. 
' Michel-Lévy, &¢., Bull. Soc. Géol. France, 3rd ser. ii. pp. 177, 189, iii. p. 287, iv. p. 730, 
viii. p.14. Scheerer, Neues Jahrb. 1873, p. 673. Dathe, Z Deutsch. Geol. Ges. 1877, 
p. 274. Details will be found in the explanatory pamphlets published with the sheets of 
the Geological Survey of Saxony, especially those of sections Rochlitz, Geringswalde, 
and Waldheim. 
