Life of the Carboniferous Period

LIFE OF THE CARBONIFEROUS PERIOD Fauna of the Marine Strata.—Numerically, the most im portant inhabitants of the clear Carboniferous seas were the crinoids, corals, Foraminifera and brachiopods. Each of these groups contributed at one place or another towards the upbuilding of great masses of limestone. For the first time in the earth's history we find Foraminifera taking a prominent part in the marine faunas ; the genus Fusulina was abundant in what is now Russia, China, Japan, North America; Valvulina had a wide range, as also had Endothyra and Archaediscus ; Saccammina is a form well known in Britain and Belgium, and many others have been de scribed; some Carboniferous genera are still extant. Corals flour ished in the clearer waters and have been used in Britain and Belgium as zonal forms. Crinoids were specially abundant in Scotland and the United States. Brachiopods reached their acme, the most important genus being Productus, now divided into several subgenera. Whilst many brachiopod species were long lived, several forms have proved useful as zonal indices, and as a supplement to coral evidence of relative time. Amongst the ceph alopods, the goniatites became abundant for the first time toward the close of the Lower Carboniferous (Visean), and swarmed in many of the marine bands of the Upper Carboniferous (Lan castrian). They are represented by several closely allied genera which exhibit distinct evolutionary trends, and furnish very deli cate zonal indices.

Trilobites were infrequent in the Lower Carboniferous, and practically extinct in the Upper Carboniferous. Fish, whilst no doubt numerous, and represented mainly by sharks, are not com mon as fossils, and their remains are usually in localized deposits, as the Red Beds of Wensleydale.

Flora and Fauna of the Continental Facies.

The strata deposited during this period are the earliest in which the remains of plants take a prominent place. The true ferns, including tree ferns with a height of upwards of 6oft., were associated with many plants possessing a fern-like habit and others whose affinities have not yet been determined. Our modern diminutive "horse-tails" were represented in the Carboniferous period by gigantic cala mites, often with a diameter of I to 2 f t., and a height of 5o to Soft. The Carboniferous forerunners of the tiny club-moss were then great trees with dichotomously branching stems and crowded linear leaves, such as Lepidodendron and Sigillaria, with trunks sometimes aft. in diameter and iooft. high.

The animals preserved include freshwater mollusca such as Anthracomya, Naiadites and Carbonicola, crustaceans and fishes. Many insects, etc., have been obtained from the coal-fields of Saarbriick and Commentry, cockroaches being especially abun dant. Land-snails have been found in tree trunks in Nova Scotia, and from the uppermost coal measures of Worcestershire. In the later Carboniferous rocks the earliest amphibians make their appearance; they were all stegocephalians (labyrinthodonts) with long bodies, bony plates on the head, and undeveloped limbs.

Economic Products.

Foremost among the useful products of the Carboniferous rocks is coal (q.v.) itself ; most of the petro leum of the Appalachian and mid-continent fields, U.S.A.—about one-quarter of the country's total; but associated with the coal seams in Great Britain, North America and elsewhere, are very important beds of ironstone, fire-clay, terra-cotta clay and occa sionally oil shale and alum shale.

In the Carboniferous Limestone series, the purer kinds of lime stone are used for the manufacture of lime, bleaching powder and similar products, also as a flux in the melting of iron; some of the less pure varieties are used in making cement. Some of the harder and more crystalline limestones are beautiful marbles.

The sandstones are used for building, and for millstones and grindstones. Crushed and screened they are often used as an aggregate for concrete. In veins in the limestone occur lead and other metallic ores, now but little worked in Britain.

BIBLIOGRAPHY.-For

a good general account of the Carboniferous Bibliography.-For a good general account of the Carboniferous system, see A. Geikie, Text Book of Geology, vol. ii. (4th ed., 1903) ; and for the American development see Pirsson and Schuchert, Text Book of Geology (2nd ed., 1924). See also Recent Additions to Geological Literature, Geological Society of London, pub. ann. since 1893. For a good account of the British coal-fields, see Coal in Great Britain (2nd ed., 1927) by J. W. Gibson, and the bibliography t0 COAL.