220 MESSES. HANCOCK AND HOWSE ON A 



which forms an important item in the section a few miles further 

 north and in the north of Durham generally. 



The Marl-slate proper equals the lower portion of No. 2 of 

 Prof. Sedgwick's section. "When closely examined, it can be 

 distinctly separated from the marly limestone, into which it gra- 

 dually passes upwards. And it is more emphatically distinguished 

 by the fossils it contains ; for, though a few stray fishes are now 

 and then found in the calcareous beds above, yet this lowest 

 part is the depository for the numerous fish- and plant-remains 

 which characterise the Permian rocks. It is then in the middle, 

 or nearly so, of this yard of Marl-slate that Mr. Duff has found 

 the remains of the Porypterus Hoffmanni, Germar, and also the 

 remains of two species of reptiles, viz., Proterosaurus Speneri, 

 H. v. Meyer, and Proterosaurus Huxleyi, nov. spec, descrip- 

 tions of which have been communicated to the Geological So- 

 ciety. Associated with these occurred numerous remains of the 

 fishes which have been so long well known, and fragments of 

 plants, a few of which are new to England, though most of them 

 have been described from the Kupferschiefer of Germany. The 

 Mollusca observed by Mr. Duff consist of fragments of Nautilus 

 Freieslebeni, Schloth., specimens of Piscina nitida, Phil., Lingula 

 mytiloides, Sow., and Myalina Hausmanni, Goldf. Of these 

 shells, only a few imperfect specimens occurred. The appear- 

 ances presented by the whole of the fossils entombed in this 

 Marl-slate seem to lead to the conclusion that this deposit was 

 formed in a very quiet estuary, into which the land reptiles, 

 the freshwater Ganoids, and the remains of coniferous plants 

 were brought, to be intermixed with other exuviae, such as the 

 shells of Nautili, Piscina}, and Lingula, which are undoubtedly 

 of marine origin. 



The Marl- slate at this spot appears to be perfectly unconform- 

 able to the Coal Measures No. 1 of the above section. But be- 

 tween it and this sandstone there is an accumulation of yellow 

 unctuous clay, about two feet thick, which has not the appear- 

 ance of an original deposit, but appears to have been formed 

 partly by the destruction of the lower part of the Marl-slate, and 

 partly by the infiltration of water carrying in clayey particles 



