Vestiges of the Natural History of Creation With a Sequel

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34 SEA PLANTs, CORALS, ETC. g-ranite The sub-groups of this system are ir. the follow. Ing succession upwards :-l, hornblende slate; 2, chiasto. lite slate; 3, clay slate; 4, Snowdon rocks (grawacke and conglomerates); 5, Bala limestone; 6, Plynlymmon rocks, (grawacke and gravvacke slates, with beds of con­glomerates.) This system is largely developed in the west and north of England, and it has been well examined, partly because some of the slate beds are extensively quarried for domestic purposes. If we ove1·look the dubi­ous statements respecting Sutherland and Bohemia, we have in this '' system" the first appearances of life upon our planet. The animal remains are chiefly confined to the slate beds, those named from Bala, in ""'.ales, being the most prolific. Zoophyta, polyparia, crinoidea, con­chifera, and crustacea,* are the orders of the animal king­dom thus found in the earliest of earth's sepulchres. The orders are distinguished without difficulty, from the ge­neral characters of the creatures whose remains are found; but it is only in this general character that ~hey bear a ge­neral resemblance to any creatures now existing. When we come to consider specific characters, we see that a diffe­rence exists-that, in short, the species and even genera are no longer represented upon earth. More than this it will be found that the earliest species comparatively soon gave :place to others, and that they are not represented even In the next higher group of rocks. One important remark has been made, that a comparatively small variety of species is found in the older rocks, although of some particular ones the remains are very abundant ; as, for Instance, of a species of asaphus, which is found between the laminre of some of the slate rocks of Wales, and th€ corresponding- rocks of Normandy and Germany, in en or .. mous q uantj hes. Ascending to the next group of rocks, we find th~ traces of life become more abundant, the number of specie~ extended, and important additions made in certain ves­tiges of fuci, or sea plants, and of fishes. This group ol rocks has been called by English geologists, the Silurian • In the Cum brian limestone occur "calarnopora;, JHhodendra, cyathophy lla, and orhicula."-Philtps. The asaphu& and trinuclP.us (crustacefl) have been found respectively in the slate rocks of Wales, and the limestone beds of the grawacke group iu Bohemia That fragments of crinoidea, though of no determinate species oc cur in this system, we have the authority of Mr. Murcbison.­Silurian System, p. 710 COMMENCEMENT OF ORGANIC LIFE. 35 Syfltem, because largely developed ~t the .surface of 2 Jis­trict of western England, formerly oc~up1ed by a. people whom the Roman historians called Stlures. Jt Is a se­ries of sandstonea limestones, and beds of shale, (harden­ed mud,) which ~re classed. in the follow~ng sub-groups, beO'inning with the undermost :-1, Llandlllo rocks (dark­ish calcareous flagstones;) 2 and 3, two groups ?alled Ca­radoc rocks; 4, Wenlock shale; 5, \Y enlock limestone; 6, Lower Ludlow rocks (shales and limestones;) 7, Ay­mestry limestone; 8, Upper Ludlow rocks (shales ar.d limestone chiefly micaceous.) From the lowest be?s upwards, 'there are polypiaria, t~ough most prevalent In the Wenlock limestone ; conch1f~ra, a ~ast n';'mber of genera, but all of the ?r?er brach.lpoda (Including tere­bratula, pentamerus, spinfer, or this, leptre~a ;) mol~usca, of several orders and many genera (including turntella, orthoceras, nautilus, bellerophon ;) crustacea, all of them trilobites (includin.6 trinucleus, asaphus, calame~e.) A little above the Llandillo rocks, there have been disc?ver­ed certain convol · 1~Pd forms, which are now est.a~hsl~ed as annelids or sea-wo .. ·ns, a tribe of creatures stall exist­ing '(nereidna and serpulina,) and which may often be found beneath stones on a sea-beac.h. One ?f these, figured by Mr. Murchison, ~s furnishe<;I with feet In vast numbers all along its body, hke a centipede. T~e occurrence of annelids is important, on account of their character and status in the animal kingdom. They are ~ed-blooded and hermaphrodite, and form a link of connex1on between the anll'Ulosa (white-blooded worm~) and a .humble clas: of the vertebrata.* TheW enlock hmestone IS most remaika­ble amongst all the rocks of th~ Silurian system, for or­ganic remains. Many slabs of It are wholly composed of corals, shells, and trilo.bite~, h_eld together b~ s~ale. 1: contains many genera of crinoidea and polypiaria, an<;I is thought that some beds of it are wholly the producbofln of the latter creatures or are, in other words, coral re.e s transformed by heat a'n d pi:essure I·n t o roc1 { S. Remain.s of fishes, of a very minute size, have b~en detected by MI. Philips in the Aymestry limestone, being apparently the first examples of vertebrated animals which breat.hed up~n our planet In the upper Ludlow rocks, remains of SIX gen· era of fi• sh have been for a 1~ onger pen•o d k n own '· they belono0- to the order of cartilaginous fishes, an order of • Such as amphioxus and myxene.