354: 



DOLOMITIC CONGLOMEEATE. 



[Ch. XXIII 



ticular species. They are often scattered through the beds singly, and 

 may be useful to a geologist in determining the age of the rock. 



Fig. 453. 



Scales of fish. Magnesian limestone. 

 Fig. 455. 



Fig. 456. 



Fig. 453. Palceoniscus comptus, Agassiz. Scale magnified. Marl-slate. 



Fig. 454. Palceoniscus elegans, Sedg. Under surface of scale magnified. Marl-slate. 



Fig. 455. Palceoniscus glapkyrus, Ag. Under surface of scale magnified. Marl-slate. 



Fig. 456. Ccelacanthus granulatus, Ag. Granulated surface of scale magnified. Marl-slate. 



' Fig. 457. 



Fig. 458. 



Pygopterw mandibularis, Ag. Marl-slate. 



a. Outride of scale magnified. 



b. Under surface of same. 



Acrolepis Sedgwickii, Ag. 



Outside of scale magnified. 



Marl-slate. 



The inferior sandstones (No. 6, Tab. p. 350), which lie beneath the 

 marl-slate, consist of sandstone and sand, separating the magnesian 

 limestone from the coal, in Yorkshire and Durham. In some instances, 

 red marl and gypsum have been found associated with these beds. 

 They have been classed with the magnesian limestone by Professor 

 Sedgwick, as being nearly co-extensive with it in geographical range, 

 though their relations are very obscure. In some regions we find it 

 stated that the imbedded plants are all specifically identical with those 

 of the carboniferous series ; and, if so, they probably belong to that 

 epoch ; for the true Permian flora appears, from the researches of 

 MM. Murchison and de Verneuil in Russia, and of Colonel von Gutbier 

 in Saxony, to be, with few exceptions, distinct from that of the coal (see 

 p. 356). * 



Dolomitic conglomerate of Bristol. — Near Bristol, in Somersetshire, 

 and in other counties bordering the Severn, the unconformable beds of 

 the Lower New Red, resting immediately upon the Coal-measures, 

 consist of a conglomerate called " dolomitic," because the pebbles of 

 older rocks are cemented together by a red or yellow base of dolomite 

 or magnesian limestone. This conglomerate or breccia, for the im- 

 bedded fragments are sometimes angular, occurs in patches over the 

 whole of the downs near Bristol, filling up the hollows and irregulari- 

 ties in the mountain limestone, and being principally composed at every 



