564 Notices from the Minute Books of the Geological Society. 



Mr. Clarke then describes in some detail the country in the immediate vicinity 

 of Cherbourg, following closely M. Alex. Brongniart's account of the physical fea- 

 tures and lithological structure of the country. 



The district consists of a succession of lofty ranges composed of quartz rock, 

 and of valleys with low hillocks of schists ; and masses of granite and trap occa- 

 sionally protrude through the other deposits. 



The schists vary in composition, being sometimes argillaceous, sometimes tal- 

 cose, also in hardness and colour. At Vasterville, to the S.E. of Cherbourg, beds 

 of grey slate and graphite ampelite contain impressions of marine plants ; and at 

 Barneville, to the south of Les Pieux, calcareous strata alternating with schist in- 

 close Terebratulse. One variety of slate, called by M. Brongniart steaschiste no- 

 duleux, consists of a base of green glossy slate, with egg-shaped nodules of quartz, 

 and passes into talc slate, which also contains concretions of felspar and crystalline 

 quartz of very variable size and form, and occasionally penetrated by the talcose 

 matrix. 



The quartz rock assumes also very different degrees of hardness, and changes 

 often in its lithological aspect. Near Vasterville it puts on the character of a fer- 

 ruginous sandstone and passes into a conglomerate ; and though these varieties 

 are stated, on the authority of M. d'Halloy, to be of frequent occurrence, yet Mr. 

 Clarke is of opinion that the ferruginous nature of the rock must be considered as 

 adventitious and of subsequent origin, being impressed also upon the schist. The 

 apparent arenaceous structure of certain beds at Le Roule is stated to disappear 

 under the lens, the whole mass presenting a vitreous fracture. The strata are 

 generally inclined at a considerable angle, but the direction of the dip varies ; they 

 are also occasionally curved. The prevailing strike of both the quartz rock and 

 the schist is from east to west. Insensible gradations from one formation to the 

 other are prevalent ; and at Rozel green schist is succeeded by quartz rock, and 

 felspar trap passes into schistose greenstone ; at Flamanville the latter rock also 

 alternates with compact eurite, which changes into rosy syenite, alternating with 

 trap, and is succeeded by regularly stratified beds of syenite, having the same direc- 

 tion with those of the quartz rock*. Mr. Clarke gives many other local details, 

 either on his own authority or that of M. Brongniart ; and then offers the follow- 

 ing genera] summary of the changes at the lines of junction. The argillaceous 

 and talcose schists, where they are in contact with the quartz rock, partake of a 

 gradual intermixture of the components of that formation, and the same strata in 

 contact with granitic rocks become charged with particles of felspar. 



That the original phaenomena took place whilst the slate was still soft and in the 

 bed of the ocean, Mr. Clarke says, there can be no reasonable doubt ; but he is of 



* See M. Brongniart's Mem., Journ. des Mines, t. xxxv. p. 119. 



