ROCKS OF NORMANDY. 263 
grauwackes much altered were noticed under redeposited Keuper 
clays; they underlie the arkoses of Montaign la Brisette *. 
The Cambrian rocks almost entirely environ the Secondary area 
on the north, south-west, and south. j 
Silurian. 
The Silurian grits of the north of La Manche do not all belong 
to the same horizon; thus the grits of Cherbourg, which rest 
unconformably on talcite at Mont Roule, of Tollevast, Sottevast, 
Lieusaint, Montebourg, &c., which contain Scolithus linearis, are 
regarded as equivalent to the English Stiper Stones. Those of 
Moitiers d’Allonne (south of Pieux) are considered as contem- 
poraneous with slaty schists with Calymene Tristan, equivalent to 
the Llandeilo Flags. The grits of Val de Cie, Vrétot, and Besne- 
ville, being of the same age as the Grés de May, are equivalent to 
the Caradoc 7. : 
The succession in ascending order is as follows + :— 
Localities. 
1. Scolithus-linearis grits, sometimes azoic, 
sometimes with Linguld............... 
2. Slaty schists and grits with Calymene Cherbourg, Siouville, &c 
b) 4) 2 
Montebourg, Cherbourg, &e. 
TU ISTTIO | Sans se hae On EAS SRR Ae 
3. Graptolite schists without Cardiola .... Yrétot, Val de Cie, Siouville, 
Besneville, &e. 
4. Grits with May fauna ..:...........c0s0ss- St. Sauveur le Vicomte. 
5. Schists with Graptolites colonus and | Varenguebec,Vrétot, St. Sauveur 
Cardiola interrupta ....ccccecveresess le Vicomte, Siouyille, &c. 
At Rufosse, nearly seven miles to the west of the east coast at St. 
Vaast, Silurian grits rest unconformably upon the Cambrian, as also 
on the hillock of Blémond in Octeville la Venelle, where the Silurian 
is represented by very compact dark-brown quartzite §. At Crasville 
I noticed a quarry of quartzite splitting up in small pieces. 
The Silurian rocks of Montebourg || occupy a tract of greater ele- 
vation than the Liassic and Triassic district surrounding them. It 
comprises the communes of Huberville, Touryille, Lestre, St. Floxel 
Quinéyville, and Octeville la Venelle. At Tourville the rock is 
often schistose, and in places constitutes great beds dipping in a 
south-westerly direction. It occupies a part of the commune of 
Quinéyille, and is prolonged thence to the isles of St. Marcouf, 
_ passing by the rock of Bavesknie, where it assumes an excessively 
compact and crystalline texture, exhibiting a kind of semifusion 
from the injection of a vein of quartz chalcedony. At Montebourg 
the rock is sometimes conglomeratic in the lower portion, con- 
taining pebbles of quartzite and decomposed felspathic rocks as well 
as fragments of talcite. Fossils are very rare in this locality. Inde- 
terminable species of Orthis have been recognized on the north- 
eastern limits of the mass. 
Near the cross-roads to Aumeville, Ozeville, Quinéville, and 
Montebourg, I observed a quarry of pale grey and whitish Silurian 
wP. 127. t P. 185, t Pp. 205, 206, § P. 196. a! P. 197. 
T 
