All rocks are necessarily composed of minerals,—that is, of certain “substances which, wherever found, present respectively nearly the same forms and physical characters, and are generally composed of nearly the same chemical constituents.” A rock may consist of one single mineral, in which case it is called a simple rock; or it may be made up of an aggregation of several different minerals, when it is called a mixed rock. Crystalline limestone, which consists exclusively of one mineral, calcite, may be given as a familiar example of a simple rock, and granite, made up of an intimate aggregation of three distinct minerals, felspar, quartz, and mica, of a mixed rock.

Those marked with an asterisk (*) are minerals,—that is, occur naturally; those with a double asterisk (**), abundantly. The others form the chemical constituents of minerals, but are not minerals themselves.

Carbonic and the Sulphuric acids also occur naturally in volcanic regions, in the form of gases. Lime, Magnesia, and Baryta are also called Alcaline Earths.

XIV. Of the elementary bodies it therefore appears that only two —carbon and sulphur—are found as minerals in any considerable quantity. In composition they are unimportant in rocks, except in the binary compounds given.

A section along the coast from Ebbs Nook to Annstead Bay, of nearly one and a half miles in length, exhibits a fine series of rocks belonging to the Mountain Limestone Formation. Thick sandstones and limestones, shales with ironstone, and coal-seams are intercalated with each other; and these strata are traversed by a lead-vein and a basaltic dyke. As we wander along the shore, we meet with evidences of sea-deposits in the limestones and calcareous shales, wherein are embedded many corals and mollusks; the sandstones, shales, and coal afford relics of the vegetation of the Carboniferous Era; some slaty sandstones give distinct indications of ancient shallow seas and coast-lines, whereon the waves broke gently and over which worms crawled; while the basaltic dyke tells of the play of internal forces, rending asunder the vast mass of stratified rocks, and pouring molten lava into the fissures.

The paleontology or the study of the fossils of Hook Head is, if it be possible, even more interesting than its physical geology. As soon as ever we cross over the sandstones, and ascend into the higher strata of the Carboniferous series proper, we reach a domain abounding with animal life. Almost immediately above the sandstones which afford the remains of the fossil plants, we reach a zone having a distinct mineral character. This zone consists of a black shale, a substance which was originally black mud deposited by the sea, and this black shale is an important member of the great Carboniferous series of the south of Ireland. At Hook, it is a very degraded form of that member of the Irish carboniferous series known under the name of “carboniferous slate.” In this locality it has a thickness of only a few yards, but westward from Hook the carboniferous slate increases in thickness, until we find it in the county of Cork, separating the sandstone strata below from the lower portion of the carboniferous limestone above, by an interval, in some instances, reaching to about 4,000 feet. At Hook, this ancient muddy sea-bottom seems to have existed for a shorter time than towards the westward, and was succeeded by a sea containing a considerable portion of lime in its waters.

There is probably no mineral, of all the many that contribute to England's commercial greatness, which is so varied in kind, chemical composition, and appearance, as coal; and an interesting volume might be written on the different forms under which it is extracted from the earth, under the names of brown-coal, oulm, cannel-coal, bituminous coal, anthracite, and the like. Next to the bituminous coals of Great Britain, the most important are the anthracites or stone-coals; and of these I propose to give a short sketch, especially as relates to their development in the coal-basin of South Wales. Of their importance commercially there can be no doubt: for, on referring to the “Mining Records” published during last year, I find that 960,500 tons were raised in this basin alone, for the purpose of supplying 18 blast-furnaces in the counties of Brecon, Glamorgan, and Caermarthen.

The learned Geologist of Montpelier, M. Marcel de Serres, has just communicated to the Paris Academy of Sciences the following facts concerning the dunes, or shifting sand-hills, of the French Mediterranean coasts. These sands are first thrown upon the shore by the sea; when dry, they are carried inward by the winds, to the distance of several kilométres, covering fields and vineyards to the depth of two or three feet, suffocating vegetation, and transforming the richest cultivation into a desert waste.