Geological Society of London. 97 
In a paper on the structure of part of the Cotentin, near Cher- 
bourg, the Rev. W. B. Clarke describes that country as consisting 
of hills or ridges of quartz rock alternating with valleys of slate oc- 
casionally associated with syenite and greenstone, which appear to 
be of posterior origin. A curious fact is mentioned: the quartz rock 
splits naturally into irregular masses, which have, nevertheless, some 
angles of fixed dimensions, namely, 103°, 64°, and 83°. Frag- 
ments of a green variety of schist exhibit the same angles under the 
same circumstances of position, proving that similar causes had acted 
on the two formations en masse, the same sets of joints, lines of strat- 
ification, and cleavage being found in both. Besides these facts, 
which are illustrated by diagrams, the author mentions others calcu- 
lated to throw light on the cleavage and jointed structure of rocks. 
PROOFS OF MODERN ELEVATION AND SUBSIDENCE. 
Under this head I shall first consider several notices of beds of | 
gravel, sand, clay, and marl, containing recent marine shells, which 
have been observed in various parts of Great Britain, a subject very 
frequently brought before our notice of late years. Deposits of this 
kind have been found by Dr. Scouler in the vicinity of Dublin, where 
they rise to the height of 80, and in some places of even 200 feet 
above the level of the sea. Besides marine shells of existing spe- 
cies, he has ascertained that some of the lower beds of this formation 
contain bones of the extinct Irish elk, by which we learn that this 
quadruped, although belonging to a comparatively modern period, 
and found_in peat-mosses, had nevertheless begun to inhabit this part 
of the world at a period anterior to some of the last changes in the 
position of land and sea, changes which are proved by the upraised 
shelly beds just alluded to. Now Professor Nilsson of Lund in Swe- 
den, although ignorant of these facts, had remarked to me that some 
great alteration must have occurred in the shape and extent of dry 
land and sea in Great Britain and the surrounding parts subsequently 
to the time when the Irish elk existed, otherwise so many entire 
skeletons of so large an herbivorous quadruped as the Cervus me- 
gaceros, would not have been found in so small an island as the Isle 
of Man. ‘That island may at no remote geological period have been 
united to the main land, and may have since been separated from it 
by subsidences, on a scale equal to the elevations of which there is 
such clear evidence in Ireland and elsewhere. 
Vol. XXXIII.—No. 1. 13 
