37 
Chalk Cliffs near Dover. 
quadrangular pyramid of an octohedron : — -these again are crossed 
at right angles by another, which is terminated in like manner, so 
that the three have one common centre : giving to the whole the 
appearance of the commencing crystallization, or the skeleton, of one 
large octohedron. Thin beds of sponges occasionally appear, their 
remains being either ochreous, or of a lighter colour than the chalk 
itself; but these are visible only when the stratum has risen con- 
siderably, and near to the beginning of the undercliff. Near the 
stream called Lidden Spout, I found the cast of a large nautilus in 
grey chalk, but much harder than that of the stratum. 
GREEN SAND AND BLUE MAKEEV 
The investigation of the chalk cliffs being my primary object, 
little attention was given to the green sand. The opportunity for 
observing its dip was however too favorable for it to be wholly 
omitted. But my interest was chiefly excited in the neighbourhood 
of Folkstone, by a considerable deposit of a marly substance over- 
lying the sand at Copt Point, and which in its natural bed is of a 
bluish colour, and in some places so moist, as to be incapable of 
bearing the weight of a man, except in dry weather, which hardens 
the surface, cracking it in every direction. My brother found that 
by submitting 100 grains of this marie to the action of acid, 13 
were lost, indicating the presence of nearly 30 per cent, of car- 
bonate of lime. 
The town of Folkstone is built upon the green sand, which is 
known in many parts of England mediately or immediately to 
underlie the chalk. It incloses beds of sandstone. The cliffs on 
the east of the town, may be in some places 80 or 90 feet high, 
the upper part of which, for a considerable distance from their ter- 
