B. Porphyritic.

C. Amygdaloidal.

This division contains similar varieties with the

last.

Fifth Division.

With a base of common felspar.

These are granitic compounds, but distinct from ejected granite. All these lavas present various modifications of external form, arising from the manner in which these have flowed, and similar to those found in the slags of furnaces.

Sixth Division.

Ejected substances, more or less altered by the

fire.

First Sub-division.

Solid: conglomerates.

A. Conglomerates of various fragments of different rocks, with mica, augit, and other minerals. B. Conglomerates consisting chiefly of clay, and having apparently, been ejccted in the state of mud. Tufa.

a. Coarse tufaceous conglomerates.

b. Fine and powdered tufa.

These latter varieties often containing augit, mica, and other imbedded minerals, as well as the solid lavas.

Loose.

Second Sub-division.

A. Fragments of various rocks, both primary and secondary, more or less altered by the fire. B. Powdery, puzzolana, dust, ashes.

The following are the chief imbedded miner

als found in these rocks.

minerals are not added.

The amygdaloidal

Many of the rocks noted under this head, have already been mentioned-but for sake of more easy reference are again introduced among the more important varieties.

These rocks occur among the primary and secondary strata, and are sometimes very limited, at others occupying extensive tracts. They may be divided into general and local.

The former constitute portions of those mixed rocks, whose origin is mechanical, and are formed of large fragments of the same substances, which, when in more minute division compose the finer strata. They must of course contain both simple and compound rocks of older origin than themselves as for example, the red sand-stones and argillites. The materials are united without any distinct cement of a crystalline nature, particularly in the secondary class: and the fragments are more or less rounded. In some instances they seem to be only portions of the finer rocks which they accompany, in others they form extensive

strata.

Local conglomerates are generally confined to the superficies of some simple rock-and are most various in lime-stones. Their composition is regulated by that of the adjoining rock. When between different rocks they contain fragments of both generally angular These remain where their parts were united but, in general conglomerates the constituents have undergone transportation. The one arising from simple fracture and re-union -the other originating from important and extensive revolutions-and may be called the consolidated ailuvia of former ages.

The minerals entering into the local conglomerates are few, and are most frequently united by distinct cement-of fine materials, or of crystalline matter, particularly among calcareous conglome

rates.

Trap conglomerates are local, and are formed by operations peculiar to those rocks-sometimes containing bituminous wood and fossil remains.

First Division.

Consisting of fragments of one rock, either imbedded in a continuous base of the same substance, or re-united chiefly by minuter fragments, or united by veins of carbonate of lime, or of quartz.

A. Consisting of limestone alone: local.

a. With angular fragments.

This occurs among primary and secondary rocks -and includes the ornamental breccia-marbles. It is local, confined to some simple limestone. The union is effected by carbonate of lime.

b. With rounded fragments.

The materials, which may be primary or secondary, have been transported. It does not occur in large strata or masses--nor attached to any particular rock, as the preceeding.

B. Consisting of fragments of quartz, or quartz rock alone united in various ways.

a. With angular fragments.

Local-connected with quartz-rock-of course

primary.

6. With rounded, or angular and rounded fragments together.

One of the varieties of quartz-rock, under which head it is mentioned.

C. Consisting of fragments of jasper, united by quartz or calcedony :-agate-local.

D. Consisting of fragments of gneiss, of various sizes, agglutinated.

This variety is local-attached to gneiss-and forms the first bed of primary sandstone, where that rock rests on gneiss: it is necessarily primary. E. Consisting of fragments of argillite, re-united by smaller particles or by clay-or imbedded in a continuous schist.

It is primary and local-and noticed under the head of Argillite. It may occur as secondary, and transported.

F. Consisting of chlorite schist formed similarly to E: local.

Accompanies chlorite schist, and is primary. G. Fragments of the different trap rocks re-united by finer particles of the same.