2.

and in strata, from This bed is eight feet

Bituminous Coal, very pure; structure slaty; three

t thick.

3. Water lime, in thin beds reposing on the coal. Lickness, six feet.

4. A Chloritic rock; color deep, almost verdigris een. Four feet thick.

5. Lias, which we have already described.

5. Calcareous tufa. It is porous, as if pierced in all ections by small worms. Six feet thick.

. Hard sparry limestone, of a light dove color, tinged h brown. Thirty feet thick.

3. Sandstone, the lower part in strata of a few inches

9. Argillaceous, loamy soil, rich, and covered with imber. Ten feet thick.

TERTIARY STRATA.

The Tertiary, or third formation, as the name indicates, vas deposited after the secondary, and may be considered s proceeding from the disintegration of this and the priseries.

mary

With respect to its relative antiquity, the tertiary is ewer than chalk, and older than the Diluvial and Alluial deposites. When these, therefore occur in the series he tertiary formations are between the chalk and the diuvium.

The Tertiary strata consists of beds of clay, sand, marl, udding-stones, and the newer limestone deposites, such s are found in the Paris basın, and in the Isle of Wight. These formations often contain abundance of fossil shells nd plants, together with the bones of fish and quadrueds. The famous locality of fossil fish at Monte Bolca, n Italy, is in tertiary strata.

In North America this formation is very extensive, reahing without interruption along the sea coast from Long sland to Louisiana and extending in some parts several undred miles inland. It consists of sand and clay often ixed with an abundance of sea shells. The valley of le Connecticut is in a considerable proportion of the same ormation, consisting of sand and clay, though the shells re absent. The whole of Long Island, Martha's Vineard, and Nantucket are also tertiary formations. In genal, tertiary strata show no marks of disturbance, being eposited since the lower rocks were disrupted.

VOLCANIC AND BASALTIC ROCKS.

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rocks

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These owe their origin to volcanic fire, and have been ther ejected from burning mountains, or forced up to the rface of the earth in a melted state by volcanic action. >me of these rocks occasionally cover all the formations therto described, and as volcanoes are still active, they

y and indeed do, cover the most recent deposites of sand I gravel.

This division is known under the name of unstratified ks, which also includes granite. Many geologists supe that granite also had an igneous origin; and this ind appears to be the prevailing opinion of the ablest ters of the day.

Basaltic or Trap rocks, including also those formed of a, cover the other formations, in a very irregular, and ertain manner. In France, large districts of country buried under ancient lava, and the northern parts of eat Britain abound with basaltic rocks.

The word trap, is said to come from the Swedish trapwhich signifies a stair, or step, because rocks of this often separate in such a manner as to form stairs. The application of this term is far from being definite, e geologists meaning by it such unstratified rocks as alt, greenstone, porphyry, and their associates; while ers have confined it to such rocks as are chiefly comed of hornblende, whether stratified or not. The forapplication of this term is undoubtedly the most comand appropriate.

'he most important volcanic rocks are Basalt, Greene, and Lava.

asalt. The color of this rock is dark grayish black, rownish gray. It is found in large shapeless masses, n columnar prisms, with from three to nine faces. se columns are of all sizes, from a few inches to sevfeet in diameter, and sometimes four hundred feet in ht. They are composed of joints, or blocks of the e angular shapes, resting one upon another. The ure of basalt is fine grained, or compact, and it often ains other minerals imbedded in it, such as felspar, tz, mica, leucite, and oxide of iron. It also exhibits ow cavities, or vesicles, apparently formed by bubbles ir during its fusion. The Giant's Causeway in the h of Ireland, is composed of basaltic columns.

reenstone. This is a compact, hard, tenacious rock dark grayish color, with a greenish tinge. It is esally composed of hornblende and felspar. This rock

beds of

or loss extent sometimes forming

stone is a common rock. The range of mountains on the west side of the Connecticut, reaching from New-Haven to Northampton, is of this rock. In some places, their height is several hundred feet. These rocks, as will be seen in another place, are undoubtedly of volcanic origin, having been elevated to their present situation through fissures, by the force of subterranean fire.

Lava. This term comes from the Gothic, and signifies to run, in reference to the flowing of volcanic matter.

The products of volcanic mountains often present very different appearances, and hence have received several names, as volcanic slags, volcanic enamel, cellular lava, compact lava, pumice, &c. But in general terms, all the liquified products of volcanoes are called lava, and for the purposes of elementary geology, this definition is perhaps

sufficient.

The colors of lava are most commonly yellowish, or greenish gray sometimes running into sulphur yellow, and grayish black. Some are compact, while others are full of small pores, and others are fibrous with a silky lustre; but all the different kinds run into each other, so that it is often difficult to make distinctions between them.

DILUVIUM.

Diluvia, or diluvial deposites, are generally supposed to have been formed during the general deluge. They consist of sand, pebbles, and blocks, or fragments of various kinds of rocks, not generally existing in the districts where these deposites are found at the present day, and hence they must have been transported from a distance. In many instances, the diluvial rocks appear to have been moved from great distances, their dimensions and situations at the same time indicating a water power of much greater force, than any which has been described, except the Noachian deluge, and it is therefore considered reasonable to attribute these effects to that cause.-See Deluge.

Class I

Order

Order

Order

ALLUVION.

Alluvia, or Alluvial deposites, are such accumulations sand, mud, and soil, together with fragments of wood, are constantly forming at the present day, by the curs of rivers and brooks, or by the rain which falls on s and mountains. These are formed by causes now stantly operating, and we have shown that considerachanges have been wrought on the earth by such

ses.

We have now given a short account of each formation, species of rock which compose the great bulk of the h. There are, however, several rocks described in e extended treatises on this subject which we have ted, and which occasionally form considerable hills, nderlay certain districts of country. This deficiency, respect to names, will be supplied by the following of M. Boue's classification of rocks, corrected and exed by Dr. Ure, of Glasgow. This contains the names I the known members of each class, and by it the stuwill be enabled to observe the synonymous terms, with lassification we have employed.