Mr. De la Beche on the Geology of Part of France. 85 



but the whole had the appearance of what is usually termed transition lime- 

 stone. I understand that it was formerly quarried as marble, for which it is 

 well adapted *. 



Quartz Rock. 



The quartz rock, in the departments of Calvados and La Manche, varies from 

 red to whitish-grey and white : it is difficult to obtain specimens, owing to its 

 toughness. It occurs generally in the form of a sandstone, but passes in some 

 instances into quartz ; and is found in beds from two to eight feet in thickness, 

 sometimes rather contorted, and frequently traversed by veins of quartz. The 

 quartz rock of the department of La Manche is described at length by 

 M. Brongniart in his memoir on the Cotentin, and named by him Quartz 

 grenu-\. The rocks exposed by the denudations in the oolite formation, in 

 the department of Calvados, are formed either wholly or in part of quartz. 



At Grouvy, a short distance from Langannerie already mentioned, this sub- 

 stance forms rough and precipitous ground, which rises above a small river : 

 the colour of the rock varies from grey to red ; the beds are from two to four 

 feet thick_, and dip at about an angle of 80° to the south. Among them is a 

 bed of iron ore about two feet thick, having the same dip and direction as the 

 rest: and when I was there, several heaps of it had been collected, but I am 

 not aware that it has as yet been smelted. These quartz beds continue to 

 Urville. 



At Potigny, on the road from Caen to Falaise, the same rock is exposed by 

 denudation, at the entrance of the village, in beds which are highly inclined, 

 and covered by horizontal strata of oolite. 



The eminence upon which stands the castle at Falaise (the birth-place of 

 William the Conqueror), and the picturesque cliff opposite to it, are composed 

 of very compact quartz rock. Upon the top of the hill leading out of Falaise, 

 on the road to Conde sur Noireau, similar beds occur : they are separated 

 from those on which the castle stands by argillaceous slate. 



Between Tourville and Mondrainville, on the road from Caen to Villers, 

 argillaceous slate and grauwacke rest upon quartz rock : the beds all dip at an 

 angle of about 45° or 50° to the north, and form part of a space exposed by 



* I am informed that this limestone is quarried very extensively in that part of Calvados which 

 is beyond the limits of the present map ; and that in character it approaches nearer to the Dudley 

 limestone than any other. Its fossils have been enumerated by M. Do Gerville. 



f Journal des Mines, Tom. xxxv. 



