8S 



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



line that separates it from the older rocks, being- much used for agricultural 

 and other purposes. It rests upon the new red sandstone formation from 

 Isigny to Villers, and, eastward of the latter place, a small portion is to be 

 traced resting upon argillaceous slate, until it is hid under the inferior oolite. 



Lias, reposing upon new red sandstone, forms the northern part of the 

 point of land between Carentan and Isigny, and is there separated from the 

 sea by a marshy and sandy flat. From the vicinity of Carentan to Fontenay 

 it forms the elevated ground behind the marshy flat which there also separates 

 the hills from the sea, and extends a considerable distance into the interior 

 of this part of the department of La Manche. 



Blue lias occurs at Ivetot, about three-quarters of a league from Valognes, 

 on the road to Briequebec, under a calcareous rock to be mentioned hereafter. 

 It is probable that from the vicinity of Carentan nearly to Montebourg it 

 rests upon the new red sandstone formation ; and it does so between Lestre 

 and Montebourg, and at Negreville, on the road from Valognes to Brieque- 

 bec. At Brevans, north-east of Carentan, it occurs above red sandstone. 

 From near Bayeux to Villers it rests upon beds of quartz gravel. 



The lias of this part of France exactly resembles that of the south of 

 England; containing, as in England, an abundance of the Gryphgea incurva 

 and Plagiostoma gigantea, with ammonites and belemnites*. I have little 

 doubt, from the information of the quarry men, that the remains of the 

 Ichthyosaurus are occasionally found in it, particularly at Brevans. 



The white and blue strata are in general much intermixed : between Port 

 en Bessin and St. Honorine white lias of considerable thickness forms the base 

 of the cliff. 



There is a fault in the lias west of Port en Bessin, which runs across two 

 small headlands. 



New Red Sandstone Formation. 



No member of this formation appears on the coast within the tract at 

 present under consideration, with the exception of some quartzose gravel 

 beds near Lestre (departement de la Manche), which are however separated 

 by a marshy and sandy flat from the sea. 



In the department of Calvados there is very little new red sandstone or red 

 marl^ except in the neighbourhood of Lison, where the elevated ground upon 



* This lias district is described very accurately, together with itsj fossils, by M. de Gerville. 

 See Journal de Physique, Tom. Ixxix. pages 18, 19, 20, and 21, Catalogues B and C; and 

 Tom. Ixxxiv. pages 209 and 210, Catalogues B and C. 



