346 



THE GEOLOGIST. 



There remain a few other facts which doubtless have an important bearing 

 on the former condition of the bone caverns. 



The stratified beds of the Plymouth limestone dip most generally to the 

 south at about the high angle of forty -five degrees ; there are, however, ex- 

 ceptions to this general rule, in certain places the beds exhibiting more or less 

 basin-shaped depressions, caused, we may legitunately presume, by the under- 

 mining of their foundation through the decomposition of the before-mentioned 

 irregularly distributed dolomite. If this be true, and similar causes have 

 tluring former geological periods been in constant operation, the entire strata of 

 this Hmestone may in their mass have undergone considerable subsidence — a 

 presumption corroborated by the presence on its northern boundary of an older 

 -series of unfossiliferous 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 they 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 would afford, moreover, the 

 necessary mechanical force required to separate in the soft and decomposing 

 slaty layers the 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, until by still further mechanical change, an entrance being given 

 to calcareous waters, they deposited the stalactite and stalagmite now some- 

 times found within them,. And it may also be deduced from such considera- 

 tions that even durmg the human period the opening of these bone caves may 

 have been possible, and that savage races using their dry and capacious cham- 

 bers as a place of residence, and leaving their easily procurable flint hammers 

 on their exit, they may, through similar chemical and 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 having the conclusiveness of 

 eye-witnesses' testimony against the contemporaneity of man with the extinct 

 mammoth and its congeners, the facts I have stated will, if properly considered, 

 tend to demonstrate that not merely is there no geological evidence whatever 

 to prove their co -existence, but that aU the apparently powerful arguments 

 based upon tlie occurrence of his remains in ossiferous caverns, may be merely 

 deceptive, and 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, there has been observed in the neighboui-hood, 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. Tliese 

 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 the formation of a large valley, through the falling in of very considerable 

 stratified masses, would naturally produce an upraising at the sides of tlie 

 depression. In the neiglibourhood 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 the high 

 strata of piu-ple slate before referred to. Following out the above'^idea, and 

 supposing that there has been in past geological time a general sinldug of the 

 land in the northern part of our hemisphere^ it is not difficult to account for a 



