THE BONE CAVES OF THE PLYMOUTH DISTRICT. 107 
derived from the rocks of the neighbourhood, and thus confirmed 
my views on this point, though we differ upon some others.* 
Now the fact that amidst all these differences there were still 
some connecting links of similarity, led me to assume on investiga- 
tion a common origin for at least the bulk of our ossiferous 
deposits. In all we have evidence of transportation by water. 
Either the bones are mixed with sand or clay, which may (as in 
the case of the red clay derived from the reddish earth of the lime- 
stone area) occasionally be of local origin, but must frequently 
have been transported for some distance ; or the remains are so 
placed and mingled that there is clear evidence of their removal 
after decay. Or we have the concurrence of both conditions. 
Finding that the variations in the phenomena of the different 
bone caverns at Oreston were as wide as those between the ossi- 
ferous deposits of Oreston generally and the deposits of the Hoe, 
while they were yet associated in the manner already described, I 
was led to suggest that " the caverns were in the main contempo- 
raneous with the surface formations [of the Hoe], and date back to 
a time when the limestone rocks which enclose the fissures were 
but slightly raised above the waters, and when therefore nothing 
was easier than the introduction into the caverns of bodies of 
animals swept down the stream, probably in times of flood, just as 
they are commonly swept down the rivers of tropical countries in 
the present day." f 
This was the first attempt at the definite correlation of our most 
important and typical series of Quaternary deposits ; and my con- 
viction that the solution of the problem here propounded is the 
true one remains unshaken. J Perhaps its bearing and importance 
will be best indicated by reference to the rival hypotheses. § 
I know of only three authorities for the opinion that any of the 
Oreston caves were dens; that is, were used as the homes of 
carnivora. 
The Eev. R Hennah, writing in 1822, supports the conjecture 
* "Brit. Assoc. Rep.," 1877, Trans. Sec, p. 68. 
t Geology of Plymouth, "Plymouth Inst Trans," vol. v. p. 475. 
"Quar. Jour. Geo. Soc.," Aug. 1876, p. 237. 
X Vide "Devon. Assoc. Trans.," vol. ix. pp. 436-440 ; vol. x. pp. 404-410. 
§ Mr. Collins comes to the same conclusion that " gravels, fissure deposits, 
and cave deposits are of the same age," and "that they helong to the mam- 
moth period." — "Brit. Assoc. Pep.," 1877, Trans. Sec, p. 68. 
