Mr. De la Beche on the Geology of Part of France. 87 



La Manche. Their boundary line would pass nearly west from the neighbour- 

 hood of Perriers to Litry, thence S. E. to Villers *, and thence E. S. E. to Croisy, 

 from whence it passes S.E., and crosses the road from Pont d'Ouilly to Falaise 

 at a little hamlet half way between the two places. 



The grauwacke, though not very abundant, may be observed in several 

 places : at the little hamlet last mentioned it is visible in beds among the slate, 

 which are highly inclined, and have a direction about east and west. 



From Conde sur Noireau to the Bruyere de Crecy the slate is disposed 

 vertically in an east and west direction ; grauwacke is observable on the 

 northern side of the latter, and may occasionally be seen among the slate 

 from thence to Croisy ; the beds are sometimes curved ; their general dip is 

 at an angle of about 45° to the north. 



At Jurigny this slate forms a small tract of country which is surrounded by 

 quartzose gravel beds of the new red sandstone formation. 



The slate near St. Lo is precisely that of the country round Conde sur Noi- 

 reau, Pont d'Ouilly, Villers, &c., and is accompanied occasionally by grau- 

 wacke. 



The slate of the north of La Manche appears to be the same as that in Cal- 

 vados ; near Cherbourg and Valognes, and in the denudations at Falaise and 

 Tourville near Caen, it is associated with quartz rock, which, as well as the 

 slate, is alike at both places. 



Near St. Vaast the slate hills end suddenly upon the low granite plain which 

 extends towards Barfleur. The slate hills on the south-west of Calvados and 

 the adjoining portion of La Manche attain considerable elevation. 



Granite. 



The granite that comes within the scope of the present communication, is 

 that which is seen a little above high-water mark at St. Vaast and Reville 

 (department of La Manche), and forms a plain at the termination of the slate 

 hills. The granite of Reville generally resembles that of Dartmoor; and, like 

 it, occasionally contains crystals of felspar as much as two inches in length. 

 This granite varies from grey to a light red tint, according to the colour of 

 the felspar. I saw no other extraneous mineral in it but tourmaline in small 

 crystals, and even these were rare. 



The granite of the coast near Reville splits in two directions ; one east and 



* Roofing slate has been quarried at Villers. 



