THE GEOLOGY OF PLYMOUTH. 
473 
The clay occurs in patches rather than beds, occasionally lenticu- 
lar. The white clay in exterior character exactly resembles the 
ordinary clays of the Bovey Heathfield, and at once suggests a 
similar origin in the decomposed felspar of the Dartmoor granite. 
This clay contains very few pebbles. The red clay, as a rule, is 
not so free from them. It may have been derived from the decom- 
position of a granite with a reddish felspar ; but the probability is 
that it owes its colour to the direct action of iron. Fragments of 
iron ore have been found in association. The white and red clays 
occur in close juxtaposition on the same level. Probably therefore 
the origin of both is the same, and the difference in colour due to 
local causes of an accidental character. 
The sand is the chief peculiarity of the series of deposits. It 
varies in colour from white, to drab, cream-colour, and red ; is 
very fine and unmistakeably siliceous — precisely such a sand as 
would be produced by the degradation of a granitic or a quartzite 
rock — such a rock, in short, as that from which the quartz pebbles 
already spoken of came. In mass it occupies a position distinctly 
subordinate to the clays, and evidently fills a large fissure in the 
rock, as yet of unknown depth. 
These deposits are by no means isolated phenomena in connection 
with the Hoe. Sand was found in digging the foundations of 
Elliot Terrace adjoining ; but that was largely mixed with pebbles. 
At the south-eastern corner of the Hoe, near the little cavern which 
is used as a tool house, the fissures in the rock contain pebbles 
precisely similar in character to those above. In such fissures we 
have the authority of Dr. Moore for saying that bones were found 
representing with tolerable closeness the Oreston fauna, including 
remains of the elephant, rhinoceros, and bear. Then again in 
1808, a deposit of sand was found on the Western Hoe, fifty 
feet above high water mark, which contained the jaw of an animal 
with teeth two inches long, and a large vertebra 9^ inches by 4£. 
Nor are such deposits confined to the Hoe. They occur elsewhere 
on the shores of the Sound. We are indebted to Mr. Spence Bate 
for the account of certain beds of freshwater sand at Bovisand, 
unquestionably of kindred and probably of contemporaneous 
origin. And at Headman's Bay may be seen the remains of a large 
" pocket" in the limestone — one side having been worked away, 
which was at least sixty feet in depth, and probably much more, 
and which was filled with clay and pebbles precisely similar to the 
