346 
THE GEOLOGIST. 
Tlici'c remain a few otlicr faets wliicli doubtless liave an important bearing 
on the former condition of the bone caverns. 
Tiie stratified beds of the Plymouth limestone dip most generally to the 
south at about the high angle of forty-five degrees ; there are, bovrever, ex- 
ceptions to tliis general ndc, in certain jilaccs tlic beds exhibiting more or less 
basin-shaped de])ressions, caused, we may legitimately presume, by the under- 
mining of tlicir foundation tlirough the decomposition of the before-mentioned 
irregularly distrn)u(ed dolomite. If this be true, and similar causes have 
during former geological periods been in constant operation, the entire strata of 
this limestone may in their mass have undergone considerable subsidence — a 
presumption corroborated by the presence on its northern boundary of an older 
series of unfossdiferous purple and grey slates of immense thickness, having a 
conforming dip of forty-five degrees, but now seen to lie at a considerably 
higher elevation. A second inference may also be deduced, viz., that, owing 
to such causes, the bone caves, at the time tliey are supposed to have been 
inhabited by carnivora, might have been situated at a much greater elevation 
than that at which we now discover them to be, affording these animals a dry 
and comfortable retreat in the mountain for devouring their prey. The dislo- 
cation of these rocks caused by their subsidence woidd afford, moreover, the 
necessary mechanical force required to separate in the soft and decomposing 
slaty layers tlie limestone beds from one another, affording in this way suitable 
openings to the animals for entrance to and egress from their caves ; the further 
subsidence again giving rise to displacements of the strata and hermetically 
closing them, untd by stUl further mechauical change, an entrance being given 
to calcareous waters, they deposited the stalactite aud stalagmite now some- 
times found ■^^^thin them. Ajid it may also be deduced from such considera- 
tions that even diu'ing the human period the opening of these bone caves may 
have been possible, aud that savage races using tlieir dry and capacious cham- 
ters as a place of residence, and leaving their casdy procurable fliut hammers 
on their exit, they may, through similar chemical aud mechanical changes, have 
once more been closed by the infiltration of stalactitic deposits. With respect, 
however to this subject, I will not dwell upon it further than to remark that, 
although we can never bring forward arguments liaving the conclusiveness of 
eye-witnesses' testimony against the contemporaneity of man with the extinct 
mammoth and its congeners, the facts I have stated wdl, if properly considered, 
tend to demonstrate that not merely is there no geological evidence whatever 
to prove their co -existence, but that all the apparently powerful arguments 
based upon tiie occurrence of his remains in ossiferous caverns, may be merely 
deceptive, aud of no real significance or certainty whatever, as their presence 
in them may be easily accounted for through the operation of natural and still 
existing causes. 
Again, tliere has been observed in the neighbourhood, and at a distance of 
not more than two miles from the above rocks, the remains of a raised beach 
on the coast fifteen feet above the present level of the ocean, and traces of 
others have been met with in various parts of the adjoining district. These 
raised beaches may at first sight appear incompatible with the view of a general 
subsidence of the neighbouring strata, but it wiU, on consideration, be evident 
that tlie formation of a large valley, through the falUug in of very considerable 
stratified masses, would naturally produce an upraising at the sides of tlie 
depression. In the neighbourhood referred to (that of the Hoe), it may be 
seen that a great part of the town of Plymouth occupies such a valley, bounded 
on the south by the limestone hills of the Hoe, and on the north by tlie high 
strata of purple slate before referred to. Following out the above idea, and 
supposing that there has been in past geological time a genei'al sinking of the 
land in the northern part of our hemisphere, it is not difficult to account for a 
