TRANSACTIONS OP THE SECTIONS. H3 



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

 former condition of the hone caverns : — 



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

 at about the high angle of 45°; there are, however, exceptions to this general ride, 

 in certain places the beds exhibiting more or less basin-shaped depi'essions, caused, 

 we may legitimately presume, by the undermining of their foundation through tho 

 decomposition of the before-mentioned irregularly distributed dolomite. If this he 

 true, and similar causes have during former geological periods been in constant 

 operation, the entire strata of this limestone may m their mass have undergone 

 considerable subsidence, — a presumption corroborated by the presence on its north- 

 ern boundary of an older series of unfossiliferous purple and grey slates of immense 

 thickness, having a conforming dip of 45°, 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 dislocation 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 dis- 

 placements 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 sometimes found within them. And it may also 

 be deduced from such considerations, that even during the human period the opening 

 of these bone caves may have been possible, and that savage races using their dry 

 and capacious chambers as a place ot 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 re- 

 mark, that although we can never bring forward arguments having the conclusive- 

 ness of eye-witnesses' testimony against the contemporaneity of man with the ex- 

 tinct mammoth and his congeners, the facts I have stated, will, if properly con- 

 sidered, tend to demonstrate that not merely is there no geological evidence what- 

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

 based upon the 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 exciting 

 causes. 



"Again, there 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 15 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 neigh- 

 bouring strata, but it will on consideration be evident that the formation of a large 

 valley through the falling in of very considerable stratified masses, woidd naturally 

 produce an upraising at the sides of the 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 the high strata of purple slate before referred to. Following 

 out the above idea, and supposing that there has been in past geological time a 

 general sinking of the land in the northern part of our hemisphere, it is not difficult 

 to account for a colder climate, though much greater elevation and more general 

 distribution of the land, prior to these changes, — and it may be easily explained 

 why raised beaches containing shells of arctic type may be compatible with such 

 general depression ; and these and other chemical changes acting below the surface 

 of the rocks, and accelerated by the mechanical opening of their fissures through 

 the freezing of water in them, may bo reasonably supposed to have in some in- 

 stances produced sudden floods of water accompanied by fields of ice, accounting 

 for the presence of remains of thick-skinned monsters in the ice and frozen soil of 

 Siberia." 



1859. 8 



