ROCKS OF NORMANDY. 261 
First. The Norman Secondary area, as far as embraced in this 
paper, does not exceed, as a rule, 100 feet above the sea *. 
Secondly. Infraliassic outliers occur at Videcosville, Octeville 
la Venelle, and St. Germain-de-Tournebut, in the north part of the 
area, and at Dezert, Brévands, and near Littry in the south; so that 
were Trias everywhere at the surface between these outliers and the 
Liassic¢ districts, owing to the gently undulating character of the sur- 
face in some cases and its plateau-like contour in others, and to the 
slight dip of the Secondary rocks, the uppermost beds of the formation 
(Upper Keuper) would alone be represented at and near the surface. 
Thirdly. M. Bonissent, commenting on the presence of a quartz 
rock of Cambrian age on the boundary of the communes of Gour- 
besville and Amfreville, says, “* Its presence in these places leads us 
to think that the Gulf of the Cotentin, in which the Keuper deposits 
were laid down, is of no very great thickness in all points where it 
is visible.” This remark applies to the whole area, as “ the 
ancient formations which formed the base of the newer sediments 
present little insulated patches, which the more recent formations 
have not entirely covered, for example, in the environs of Monte- 
bourg, Valognes, Lieusaint, Rauville la Place, Magneville” t; add 
to these the quartz-porphyry of St. Colombe, the Cambrian limestones 
of Cavigny and La Meauffe, the Silurian inliers of Colomby and 
Flottemanville +, and the paleozoic patches near Littry. 
Making, therefore, due allowance for depressions in their bed, the 
Triassic rocks of Normandy can scarcely exceed 200 feet in maxi- 
mum thickness, whilst their mean thickness is probably less than 
100 feet. Iam therefore forced to regard them as a part only of 
the Upper Keuper, which in the Devon and Somerset area south of 
the Mendips appears to present a mean thickness of about 700 feet ; 
so that even if the rocks of Normandy attained 300 feet, that thick- 
ness would not represent the whole of the Upper Keuper division. 
Third Proposition. 
If this reasoning is conclusive, it follows that the present extent 
of Normandy was not submerged until after the deposition of the 
earlier sediments of the Upper Keuper, and in no case could it have 
been under water during the formation of the pebble-beds of Devon 
which constitute the base of the Lower Keuper sandstones; so that 
there are strong grounds for entertaining the conclusion set forth 
in my third proposition, “ that fragments from the Palsozoic rocks 
of Normandy (in its present extent) were never incorporated in the 
Triassic sediments of Devon.” 
Fourth Proposition. 
I now come to the concluding proposition, that the foreign 
fragments in the South-Devon Trias were derived from rocks in the 
Channel area, the existence of which is proved by the nature of the 
Paleozoic areas of Normandy, Devon, and Cornwall. I shall first 
mention briefly the varietics of Palseozoic and igneous rocks of 
* Bonissent, op. cit. p. 6. t Ib. p. 264. t Jb. p. 192. 
Q.J.G.8. No. 1388. T 
