22 



THE GEOLOGIST. 



XVIII. — Spirifetiina insculpta. Phillips. PI. xii., fig. 35. 



Spirifera insculpta, Phillips, Geol. of Yorkshire, vol. ii., p. 216, pi. ix., figs. 

 2, 3, 183G; and Dav. Mon. Garb., p. 42, plate vii., figs. 48-55. 



In shape it is more or less semi-circular, and about one-third wider than 

 long ; the hinge-area is straight and as wide as the greatest width of the shell. 

 The area large, triangular, and but slightly curved ; beak small, and not much 

 produced. Both valves are about equally convex ; the ventral one is 

 ornamented with five (rarely seven) large bold angular ribs, of which the 

 central one exceeds the others somewhat in proportion, and corresponds with a 

 deep angular sinus in the opposite valve. All the ribs are sculptured, or 

 closely mtersected with small concentric laminae, which give to the perfect 

 shell a very elegant appearance. This is a rare Scottish shell ; it occurs at 

 Gare, in Lanarkshire, at two hnndi-ed and thirty-nine fathoms below the " EU 

 coal." 



Pamily Rhynchonellid^. 



Of this family the genera Rhijnchonella and Camarophoria alone have been 

 hitherto discovered in the Scottish carboniferous strata. Of the first we know 

 but two species, and one only of the second ; while m England eight of Rhyn- 

 chonella and three of Camarophoria have been found. 



Genus Rhynchonella. Pischer. 1809. 

 The shells composing this genus vary much in their external shape and 

 appearance, some being transverse, others rounded or angular, smooth, variously 

 ribbed, or striated. The valves are generally convex, with or without a mesial 

 elevation or sinus ; the beak is acute, prominent, or so greatly incurved as to 

 touch and even to overhe the umbone of the opposite valve ; the foramen is 

 variable in its dimensions and shape, being placed under the extremity of the 

 beak, and entirely or partially surrounded by a deltidium. The sheU-structure 

 is fibrous and not perforated ; and the valves articulate by the means of two 

 teeth in the ventral, and corresponding sockets in the dorsal valves. The 



is perhaps more correct to separate them into two. The Carboniferous, or Hiljemian hme- 

 stone is fifty feet thick at DrumgTiin in Tyrone, it is about fifteen hundi-ed feet thick at Black 

 Head in Clare, and occupies above twenty thousand square miles iu Ireland. This greatly 

 predominates ; the coal-measures are two thousand feet thick, or more. The Old Red sand- 

 stone, at Kildress in Tyrone, and the Old Red Sandstone of Herefordshire are two very dif- 

 ferent things. The first belongs to the Carboniferous system ; the latter is a subdivision of 

 the Silurian rocks." 



My mistake was not therefore in in the order of superposition of the different strata, 

 which Mr. KeUy admits to be correct ; but in having endeavoured to reconcile the succession 

 of the Carboniferous strata in Scotland with that of Ireland by applying Mr. Page's general 

 denomination of "Lower Coal-measures" to that group wliich embraces all the alternations of 

 strata which he between the Old Red Sandstone and the mountain- or Carboniferous- 

 limestone. The term, however, would not apply to Ireland, since in the sister island no 

 lower coal-measures underhe the mountain-hmestone, as we find to be the case in Scotland, 

 and where Mr. KeUy suggests that the limestone may be moved up a stage, with coal- 

 measm'es below it. It must appear evident to aU that the term Old Red Sandstone cannot be 

 retained for a Silurian, Devonian, and Carboniferous rock, and tliis is the reason why I was, 

 and stiU am, so averse to applying the term, or forming a subdi-sdsion by that name for those 

 Irish red and yellow sandstones full of carboniferous fossils ; for if the Calciferous- and 

 moimtain-lime stone might, according to Mr. KeUy's own statement, be imited into a single 

 division on account of the similarity of theh fossils, as a pala?ontologist, I should add that 

 the same rea,soning might equally weU apply to the red sandstone of Kildi'ess, for there also 

 we find exactly the same fossils as those which occur in the calciferous and carboniferous- 

 limestone. I shoiJd therefore suggest that geologists should di-op the tenn "old," and 

 in their subchvisions of the Carboniferous group say, 1, Lower carboniferous red and yel- 

 low sandstone ; 2, calciferous slate ; 3, carboniferous-limestone; and, 4th, coal-measures, by 

 wMch means the vexed question relative to the Old Red Sandstone woiild not be interfered 

 with as fiir as the Carboniferous system is concerned. It is also weU 1viio\to that ]\Ir. KeUy is 

 of opmion that no Devonian rocks occm- in Ireland ; wliile Sir R. Murchison beheves that 

 there exists there also a series of many thousand feet of shales and grits above the highest 

 Upper Silurian wliich represents precisely in time the mass of the Devonian rocks ; tliis, 

 however, has nothing to do with the red and yeUow sandstone of Kildi'css which mi- 

 doubtcdly forms pai't of the Carboniferous system. 



