near to trap is often highly indurated, assuming the character of chert.

Third Division.

Compound : containing some visible ingredient intermixed.

A Limestone containing mica.

B. Limestone containing mica and sand.
These occur with mica or micaceo-arenaceous

shale.

Fourth Division.

Containing fragments of limestone, or of quartz,

or of different compound rocks.

Conglomerated. A. Containing fragments of previous limestone. B. Containing fragments or pebbles of quartz. C. Containing chert or agate in fragments. D. Containing fragments of argillite.

There are other divisions of limestone, often well marked; sometimes arising from actual change ofcharacter, from the presence of fossil contents, or from color: mostly however these names are local or geographical: the latter is perhaps the safest, as it can always be referred to and known.

SYNOPSIS OF SAND STONES.—(SUPERIOR.) The term superior sandstones is here used

as the Divisions of these sandstones are different from, and above the old red sandstone.

First Division.

Simple: of quartz alone.

A. An aggregate of grains of quartz, more or less condensed, and varying in hardness.

a. Of a large grain; gravelly.

b. Fine, arenaceous.

The brillancy of these varieties, which are almost necessarily white, varies according to the quality of the quartz from which they are formed. When highly indurated, their position alone distinguishes them from quartz rock. In the vicinity of trap, they are said to be indurated occasionally to the state of common quartz.

Second Division.

Compound: of two or more ingredients.
A. Quartz-sand and carbonate of lime.
a. Large grained, gravelly,

b. Fine, arenaceous.

These are generally white.

B. Quartz sand with clay.

Subdivisions a. and b. as the preceding.

The colors vary: white, ocre yellow of different hues, or red, or grey, or greenish, or black:

occasionally mottled or striped. The red varieties, and sometimes even the white and grey are distinguishable from the old red sand stone, only by their geological position, and this it is sometimes impossible to ascertain.

C. Quartz sand with schistose clay.

The clay is more or less interlaminated and the rock passes into shale.

D. Quartz sand with clay and carbonate of lime, Subdivisions a. and b. similar to var. A. and B. E. Argillaceous or calcareo-argillaceous sandstone mixed with bitumen.

This sometimes passes into bituminous shale. F. Quartz sand with clay and mica, or with clay, carbonate of lime, mica and red oxide of iron.

The red marle, or new red sand stone of Enggland, is of this kind.

G. Quartz sand with carbonate of lime, mica and green earth, called in England Kentish rag.

H. Sandstone of various qualities containing a large portion of rust of iron, which often forms the cement of the other ingredients: ferruginous sand

stone.

The varieties of this division, like those of the preceding, when in contact with trap, are said to pass into jasper or chert. They sometimes contain pyrites, carbonate of copper, oxide of cobalt, and oxydulous iron.

D. Sandstone containing fragments of schistose clay or shale, or of limestone, or of both.

E. Sandstone containing flints. English puddingstone. This is occasionally of a loose arenaceous texture; or is highly indurated. Doubtful if it is not alluvial.

SYNOPSIS OF CLAY

The clay and the marle and sand mentioned in the following synopsis belong mostly to the Tertiary formations.

A. Ferruginous clay: scarcely ever plastic, red or yellow.

B. Fuller's earth: dull green or grey: semitransparent, and crumbling when in water. Occurs in the upper sandstones, in the limestones and new red marle,

C. Schistose clay: white or grey scarcely ever plastic, until after exposure to air, when it crumbles. Pipe clay, often above the chalk.

D. Indurated, generally in irregular nodules; very refractory in the fire. Stourbridge clay.

E. Plastic clay, potter's clay, of various colours and properties. Very similar to var. C. New Jersey clay.

F. Blue clay: London clay: plastic in various degrees.

There are other varieties of clays, passing into different substances-besides lithomarge, tripoli, &c.

SYNOPSIS OF MARLE.

A. Simple, or earthy: consisting principally of calcareous matter.

a. Massive, more or less compact.

b. Schistose-marie slate.

c. Powdery, or imperfectly plastic, with few or no fragments of shells: often much mixed with sand and clay.

d. A congeries of shells and fragments of shells, more or less pure Shell-marle of agriculturalists. New Jersey, &c. Some of the varieties, a & b. become plastic on exposure to air.

B. Bituminous marle: more or less distinctly schistose. There is some obscurity in this substance, since it is known to contain fish, and it is