268 



THE POPULAR EDUCATOR. 



limestone when it assumes a crystalline state a name taken 

 from that of the French geologist, M. Dolomieu. 



Towards the close of the Permian period Western Europe 

 seems to have been more than usually affected by the elevation 

 forces which have been in constant operation, for we find that 

 the upper members of the limestones have, about the time of 

 their consolidation, undergone a severe disturbance, so severe, 

 indeed, as to break up their whole mass into " breccia" angular 

 fragments about two feet in diameter. This phenomenon is 

 often exhibited on the coast near the mouth of the Tyne. The 

 fragments are never water-worn, but the agitation which made 

 them passed away, and they were left undisturbed, to be re- con- 

 solidated by fresh deposit of a similar nature. 



This brecciated formation also occurs in patches over the 

 downs near Bristol, where it fills up hollows in the mountain lime- 

 stone. In all cases the fragments are the debris of the rock on 

 which the limestone rests, cemented together by a late deposit. 



From the internal evidence of the rocks it would appear that 

 the limestone strata, No. 1 in the table, was formed in shallow 

 water, whereas that immediately underlying the brecciated 

 limestone the fossi- 

 liferous limestone is 

 a deep-water forma- 

 tion. We judge this 

 from the absence of 

 corals and the ripple 

 marks which the slabs 

 of the uppermost 

 limestones sometimes 

 axhibit. But in No. 

 3 many beautiful 

 specimens of bryozoa 

 are detected. Fig. 97 

 represents the Fene- 

 stella retiformis, which 

 appears in many dif- 

 ferent shapes, and 

 bears as many dif- 

 ferent names. Each 

 of the little pits was 

 a cell inhabited by a 

 polyp, and the fossil 

 represents the work 

 of a whole nation of 

 the little people, 

 carried on in the 

 quiet waters of the 

 ocean depths. The 

 flora of the Permian 

 period will be illus 

 trated in a sketch of a 

 forest of the period 

 in our next lesson. Its fauna is like that of the late palaeozoic 

 era, the fish still retain the heterocercal tail ; but after this wo 

 shall find the homocercal tail gains the ascendancy, until in our 

 own time only a very few heterocercs exist. The occasional and 

 doubtful indications of air-breathing reptiles which the carboni- 

 ferous beds afforded are now confirmed by the appearances of 

 many fossils the Palceosaurus, the Protosaurus, the Thecodonto- 

 sauras. The thecodont-saurians (sheathed-toothed saurians) 

 appear to be peculiar to the Permian period. The Productus 

 horridus (Fig. 98) and the Spirifer undulatus (Fig. 99) are 

 characteristic fossils of the period. 



From what we have said the Permian will be seen not to have 

 any very striking features. A few veins of lead and zinc tra- 

 verse the magnesian limestone, but the rocks of the period aro 

 anything but rich in metalliferous deposits. 



Perhaps the Permian is most celebrated for its building stone, 

 inasmuch as the Houses of Parliament are constructed of it, but 

 it is an honour which the stone has ill deserved, for it cannot 

 stand the atmosphere of London. 



PERMIAN FOSSILS. 



Those in italics appear for the first time ; those marked with 

 an asterisk do not exist beyond the period. 



Plants. Caulerpites, Confervites, Voltzia, Neuropteris Huttoniana, 



* Neuropteris, * Sigillaria, * Stigmaria. 

 Foraminifera. Dontalina, Spirillina, Texularia. 



Corals. Polyccelia, *Aulopora, * Choetetes. 

 Polyzoa. Si/nocladia, * Fenestella, * Glauconome. 

 Brachiopoda. * Producta, * Strophalosia, Spirifer. 

 Conchifera. Bakewellia, Schizodus, Cardiomorpha, * Axiniis. 

 Gasteropoda. Turbo, Loxonema, Euornphalus, Pleurotomnria. 

 Cephalopoda. Nautilus Bo werbankianus. 

 Echinoderrnata. * Cyathocrinus. 



Reptiles. Labyrinthodon, Pateosaurus, TJiecodontosaurus. 

 Fish.Gyropristis, *Platysomus, *Pala3oniscus, *Pygopterus. 



THE TEIASSIC GROUP. 



The succession of strata occupying a position between the lia* 

 and the carboniferous formations is more or less tinted witt 

 the oxide of iron, and, as the sandstones are somewhat promi- 

 nent, geologists were in the habit of distinguishing the forma- 

 tion from the masses of red sandstone which underlie the coa! 

 period by naming the one the New and the other the Old Bed 

 Sandstone. As the examination of the strata became more 

 careful, the new red sandstone was clearly capable of a sub- 

 division into upper, middle, and lower groups. As far as the 

 lithological character of the rocks is concerned, this division 



might have been re- 

 tained ; but when the 

 life of the period, as 

 exhibited in its fossils, 

 was more fully under- 

 stood, it was found 

 that the fossils of the 

 upper group evidently 

 were more akin to 

 those of the lias above 

 than to those of their 

 nearer neighbours, 

 the middle and lower 

 new red sandstones. 

 In nothing was this 

 more evident than in 

 the fish. During the 

 carboniferous period 

 the fish life had 

 reached its maximum , 

 and began to declire 

 at the close of that 

 era ; yet the hetero- 

 cercal tail was the 

 distinctive character- 

 istic of the fish, and 

 continued to be so 

 through the lower and 

 middle groups above 

 alluded to. However, 

 upon passing into 

 the upper group, the 



homocercal tail begins to take the place of the more highly- 

 developed heterocercal, and hence there is a very evident line of 

 division running between the upper and middle of the three 

 groups. Below this line the strata contains life of palaeozoic 

 types, and above it the new phase of life is termed mesozoic ; 

 or, according to another nomenclature, the Permian is the upper- 

 most formation of the primary strata, while the Trias or upper 

 group of the new red sandstone is the lowest member of the 

 secondary strata, which contain the fossils of the mesozoic life. 

 The Trias, as a group, is very imperfectly developed in Eng- 

 land, but in Germany the formation is well exhibited. Its 

 rocks form no exception to the rule that the clays, the lime- 

 stones, and the sandstones have each their representatives. 

 But the three are so distinctly arranged that the formation has 

 been named Trias from the fact. The limestone deposit of the 

 group is wanting in England ; and seeing that the best fossils 

 are preserved in the limestone rocks, we are deprived of aa 

 extensive a knowledge of the flora and fauna of the period as 

 we possess in other cases. 



As Germany is the ground where the Trias is typically deve- 

 loped, the German nomenclature is usually adopted. The fol- 

 lowing table exhibits the divisions of the formations, with their ' 

 English equivalents : 



Keuper .... Saliferous and gypseous shales and sandstones, 



JfuscTielfealfe . . Wanting in England. 



Hunter -sandxtein . Sandstone and quartzose conglomerate. 



