The Secondary Rocks, in which our further researches are to be prosecuted, consist of a great and varied series, resting, generally unconformably, against flanks of the upturned primary rocks, sometimes themselves considerably inclined, at others, forming extensive basin-like beds, nearly horizontal; in many places much broken up and shifted by disturbances from below. They have all been formed out of the materials of the older rocks, by virtue of the wearing power of air and water, which is still every day carrying down vast quantities of the elevated matter of the globe into the sea. But the separate strata are each much more distinct in the matter of its composition than might be expected. Some are siliceous or arenaceous, (sandstones,) composed mainly of fine grains from the quartz rocks — the most abundant of the primary strata. Others are argillaceous—clays, shales, &c, chiefly derived, probably, from the slate beds of the primary series. Others are calcareous, derived partly from the limestones, and partly eliminated from the waters of the ocean by organic life. As a general feature, they are softer and less crystalline than the primary rocks, as if they had endured less of both heat and pressure than the senior formation. There are beds (coal) formed solely of vegetable matter, and some others in which the conspicuous ingredient is a carbonate of iron, (the black band.) The secondary rocks are quite as communicative with regard to their portion of the earth's history as the primitive were.