E. The mica imperfectly parallel and scaly, bent round the grains of quartz, giving a peculiar character to the rock in the transverse fracture.

Second Division.

Composed of three or more ingredients.

A. Many of the preceding varieties containing crystals or concretions of hornblende.

B. The same containing felspar, and passing into gneiss.

C. Containing chlorite or talc in addition, and passing into chlorite schist, or talcose schist.

D. Irregularly compounded with more than one of the above-named ingredients.

E. Containing carbonate of lime, with the usual ingredients, and giving it the appearance of gueiss.

Third Division.

Conglomerated.

Containing superadded fragments of granite, quartz rock, limestone and other substances.

SYNOPSIS OF ARGILLITE.

First Division.

Simple of indurated shistose clay alone. A. Straight fissile, or continuously laminar.

a. With a straight even fracture on the laminæ.

b. With a rough and undulated fracture. The varieties form roof slate..

B. Imperfectly fissile, or massive slate.

a. Amorphous, sometimes breaking more easily in one direction than another.

b. Fibrous.

c. Massive, splitting with curved surfaces. d. Black, imperfectly fissile, of dull earthy aspect.

e. Black, and so soft as to mark paper: black chalk or drawing slate Some varieties are fissile. f. Spheroidal concretions embedded in the laminar varieties.

C. More compact, with a smooth splintery, or minutely granular and splintery fracture, translucent on the edges. Whet slate, or hone.

a. Compact, imperfectly fissile, the fragments translucent, and much resembling compact felspar -common hone.

b. Laminar or scaly; straight or undulated, the fragments translucent-used as hone.

c. Granular, rough: less translucent.

D. So hard as to strike fire easily; but the particles of quartz not visible.

This is the flinty slate or siliceous schist of some

writers.

Second Division.

Compound: indurated schistose clay, with some other ingredient conspicuously mixed. A. Simple argillite and mica.

a. The mica extremely thin and broad: passes into micaceous schist: the lustre silky or plumbaginous.

b. The scales of mica minute, intermixed irregularly, or in laminæ. The fine greywacke

schist of some writers.

B. Simple argillite and talc; of a greasy feel, and silky lustre passes into talcose schist. C. Simple argillite intermixed with chlorite.

a. The chlorite invisibly minute, as if powdery, the fracture dull and earthy.

b, The chlorite foliated, or scaly, and the fracture glossy.

These varieties pass into chlorite schist.
D. Simple argillite with hornblende.

a. The hornblende in minute scaly crystals,

or irregular grains, or flat plates.

b. The hornblende fibrous : fascicular: or else straight, or curved, and radiated.

Some varieties of a. pass into hornblende schist.

E. Argillite, A. div. 1st, intermixed with quartz, a. An uniform mixture of sand and blue clay : imperfectly schistose, and resembling an argillaceous sandstone.

b. Argillite, massive, or laminar, mixed with quartz sand. The fine greywacke and greywacke schist of some writers.

c. Quartz gravel of various sizes, similarly intermixed: coarse greywackes.

F. Argillite, C. div 1st, intermixed with quartz.

a. With very fine grains or powder of quartz. Not fissile: fracture sometimes rough and splintery, and often resembling the fine and grey varieties of sandstone.

b. With visible grains of quartz of different sizes, and resembling the coarser sandstones. This also is termed greywacke.

G. Argillite, with embedded particles of calcareous spar.

H. Argillite, with embedded felspar, in crystals or fragments, having a porphyritic appearance.

Third Division.

Of argillite, with two or more ingredients.

A. Argillite with quartz sand, and mica.

4. Schistose.

b. Massive.

Occasionally termed greywacke.

When the

quartz is abundant, they pass into micaceous

sandstone.

B. Argillite with quartz and felspar.

C Argillite, with quartz, felspar and mica.
These form other varieties of greywacke.

Fourth Division.

Containing fragments of the same or of other compound rocks of a conglomerate structure. A. Fragments of argillite re-united.

:

a. schistose; slaty.

b. Imperfectly schistose; or massive. B. Fragments of quartz united by argillite. a. With simple argillite.

b. With any of the compound varieties. C. Fragments of quartz and of schistose slates, united by var. C. div. 1st-massive.

D. Quartz, felspar, and clay slate in minute fragments; united, with or without any additional argillaceous cement.

E. Fragments of quartz and basalt, cemented by a mixture of clay slate and quartz sand.

F. Fragments of jasper and clay slate, with grains and fragments of felspar and of quartz, united by a siliceo-argillaceous base.

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