262 W. A. E. USSHER ON THE TRIASSIC 
La Manche, commencing with the igneous. According to M. Bo- 
nissent *, granite and associated granitoid rocks (syenite, diorite, 
pegmatite, amphibolite, fraidonite, harmophonite, petrosilex, pro- 
togine, protogenic, syenitic, dioritic, and petrosiliceous porphyries, 
syenitic granite, and serpentine) form a great part of the coast 
from Sciotot (near Pieux) on the west to St. Vaast on the east. 
The patches of porphyry in the tract limited on the south by 
Coutances and St. Lo, and on the north by a line from Vasteville by 
Thiel to St. Vaast and Morsalines, are cited? as examples of M. Du- 
fresnoy’s opinion, that they represent “‘ the vents of a great interior 
mass of porphyry, whose eruptive force had been sufficient to disturb 
and fissure the rocks of older date, but too feeble to open a large 
outlet for widespread ejection.” 
Speaking of the granitic and porphyritic rocks of La Manche, 
M. Bonissent ¢ says :— These different groups are but very small 
portions of the great mass of which they ought to form part, judging 
from the different isolated veins with no apparent connexion with 
the principal groups. As also the islands and rocks between the 
Channel Islands and the most westerly point of England are formed 
of granite, and as the same rocks almost exclusively form the coast 
from Brest to St. Malo, and, in England, have in several places 
pierced the primitive formation, it is easy to conceive that all these 
veins, rocks, and groups are connected with one and the same 
granitic formation, in part hidden beneath the sea.” 
Talcite. 
The north coast bounding Cherbourg Bay, from Bretteville to 
Omonville, a distance of nearly twenty miles, is composed of 
talcites. At Airel, in the district of St. Lo, talcites were recog- 
nized at a depth of nearly 33 feet beneath the Cambrian from the 
surface. 
Mica-schists occur in the neighbourhood of Coutances, also 
gneiss, which is likewise found near Cherbourg, Pieux, &c.§ 
Cambrian. 
The Cambrian rocks of La Manche are divided into two stages— 
the Upper consisting of anagenites, conglomerates, and various 
grits (arkoses), the Lower of phyllades and grauwackes ||. 
Arkoses and anagenites are well developed in the north of the 
Cotentin, from Morsalines, on the north-eastern confines of the 
Secondary area, to Cape la Hogue]. In the latter locality phyl- 
lades and grauwackes are but sparingly distributed. In one spot 
in the commune of Kculleville they are accompanied by a reddish- 
brown crystalline limestone **, 
The schistose character of the taleose rocks nearly always dis- 
appears in the arkoses and anagenites Ty. 
By the road to St. Vaast, at the entry of Valognes, phyllades and 
* Op. cit. p. 31 &e. i) Bag ip dey 12 
4 B pp.103, 104. P, 122 q P. 138. *e P, 194, 
