8C^ Mr. De la Beche on the Geology of Part of France. 



a denudation in the oolite formation. The relative position of the quartz rock 

 and arg^illaccous slate between Mondrainville and Tourville and at Falai.se, 

 Avould lead to the conclusion that they alternate here, as they do between 

 Valognes and Cherbourg-. The general character of the slate is well dis- 

 played at the mountain of Le Roule behind the last-mentioned town ; where it 

 varies from red to grey, the grey being often as compact as cjuartz ; the beds 

 are sometimes several feet in thickness, and frequently curved ; their dip is 

 between 45° and 50° to the north. 1 observed in the quartz rock of Le Roule 

 the cylindrical bodies mentioned by Dr. M^CuUoch as occurring in the quartz 

 rock of Glen Tilt *. On that part of the hill over which the road to Valognes 

 passes, about a league and a half from that place, the quartz rock alternates 

 with argillaceous slate. 



There is much (juartz rock in the vicinity of the latter town ; it constitutes 

 the high hill between Valognes and Montebourg ; on the top its beds are 

 nearly white. At the high hill between Lestre and Montebourg-, which is also 

 composed of it, the beds are mostly grey, sometimes red ; they vary conside- 

 rably in thickness, and dip to the east at about an angle of 45°; the same beds 

 continue to Greneville (on the coast between St. Vaast and Lestre), where they 

 probably rest upon argillaceous slate. 



Near Negreville, on the road from Valognes to Briequebec, and from 

 thence to the latter town, a series of rocks occurs, which may generally be 

 referred to quartz rock, but which, in part, very much resemble old red sand- 

 stone, being micaceous, and of the usual colours and character of that rock : 

 this sandstone (if really such, and not a variety of quartz rock) either alternates 

 with or passes into quartz rockf. 



The direction of the beds near Negreville is fromE.N.E. to W.S.W. ; 

 their dip is to the E.S. E. at about an angle of 80°. 



At the mountain of Le Roule, and at the high ground between Lestre and 

 Montebourg, thin beds of sandstone, which are in general red, slaty, and not 

 very compact, occur in the quartz rock. 



Argillaceous Slate and Grauwacke. 



A considerable portion of the south-western part of the department of Calva- 

 dos is formed of these rocks, which are continued into the department of 



* Geological Transactions, Vol. iv. p. 269. 



f Dr. M'CuUoch mentions an alternation of old red sandstone with quartz rock, as occurring 

 ju the Isle of Sky. Geological Transactions, Vol. iv, p. 273. 



