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Show 42 SECONDARY ROCKS.-ERA OF THE CARBO .. NIFEROUS FORMATION. LAND FORMED.-COMMENCEMENT OF LAND PLANTS \VE now enter upon a new great epoch in the history of our globe. There was now dry land. As~ co~sequence of thi::; fact, there was fresh water, for ram, Instead of immediately returning to the sea, as formerly, was .now gathered in channels of the earth, and became spnngs, rivers and lakes. There was now a theatre for the existenc~ of land plants and animals, and it remains to be inquired if these accordingly were produced. The Secondary Rocks, in which our further researches are to be prosecuted, consist of a great and varied series, resting, generally unconfqrmably, against flanks of the upturned primary rocks, sometimes themselves considerably inclined, at others, fanning 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 \'ast 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 miO"ht be expected. Some are silicious, or arenaceous (sa~dstone,) composed mainly of fine grains from the quartz rocks-the most abundant of the primary strata. Others are ar~llaceous-clays, shales, &c., chiefly d~rived, probably, trom the slate beds of the prim~ry senes. Others are calcareous, derived from the early limestone. As a general feature, they are softer and less crystalline than the primary rocks, a~ if they had endured less of both heat and pressure than the senior formation. There are beds (coal) formed solely of vegetable matter, and ~orne others in which the main ingredient is particles_of Iron (the iron black band.) The secondary rocks are qmte as communicative with regard to their portions of the earth's history as the primttive were. . The first, or lowest group of the sec.ondary rocks, IS called the Carboniferous ~Fo'rmation, from the remarkable feature of its numerous intPrspersed beds of coal It commences with the bP.d.s of the mountain limestone, COMMENCEMENT OF I ... AND PLANTS. 43 which. in some situations, as in Derbyshire and Ireland, are of great thickness, being alternated with chert, (a siliceous sandstone,) sandstones, shales, and beds of coal, generally of the harder and less bituminous kind, (anthracite,) the whole being covered in some places by the millstone grit, a siliceous conglomerate composed of the detritus of the primary rocks. The mountain limestone, attaining in England to a depth of eight hundred yards, greatly exceeds in volume any of the primary limestonebeds, and shows an enormous addition of power to the cause formerly suggested as having produced this substance. In fact, remains of corals, crinoidea, and shells, are so abundant in it, as to compose three fourths of the mass in son1e parts. Above the mountain limestone commence the more conspicuous coal beds, alternating with sandstones, shales, beds of limestone, and ironstone. Coal is altogether composed of the matter of a terrestrial vegetation, transmuted by pressure. Some fresh-water shells have been found in it, but few of marine origin, and no remains of those zoophytes and crinoidea so abundant in the mountain limestone and other rocks. Coal beds exist in Europe, Asia, and America, and have hitherto been esteemed as the most valuable of mineral productions, from the important servir.es which the substance renders in manufactures and in domestic economy. It is to be remarked, that there are some local variations in the aiTangement of coal beds. In France, they rest immediately on the granite and other primary rocks, the intermediate strata not having been found at those places. In America, the kind called anthracite occurs among the slate-beds, and this species also abouncts more in the mountain limestone than with us. These !ast circumstances only show that different parts of the earth's surface did not all witness the same events of a certain fixed series exactly at the same time. There had been an exhibition of dry land about the site of America, a little earlier than in Europe. ~ome features of the condition of the earth during the deposition of the carbomferous group, are made out with a clearness which n1ust satisfy most minds. First, we are told of a time when carbonate of lime was formed in vast abundance at the bottoms of profound seas, accompanied by an unusually large population of corals and encrinites; while in so1ne parts of the earth there were patches oi dry land .. covered with a luxuriant vegetation. Next, we |