92 TllK lli:v. a. U. HALL, F.S.A., 



one-eighth of an inch, or say one-huncli'edth of a foot, has been 

 deposited in that length of time (Brit. Association Report, 1869, 

 p. 196). This gives a foot in twenty thousand years, or live 

 feet in one hundred thousand years ; and there is no reason what- 

 ever to consider this to be too high an estimate to account for the 

 triple change of organic remains, of climate, and of physical geo- 

 graphy. But below this again there is another and much older 

 layer of stalagmite, generally broken up and imbedded in the 

 cave earth. This older stalagmite is very thick, and is much 

 more ciystalline than the uppci* one, so that it was probably 

 formed at a slower rate. Yet below this again, in a solid brec- 

 cia, very different from the cave earth, undoubted works of ail 

 have been found. A fair estimate will therefore give us, say, 

 one hundi-ed thousand years for the upper stalagmite, and about 

 two hundi-ed and fifty thousand for the deeper layer of much 

 greater thickness, and of more crystalline texture. But between 

 these we have a deposit of cave-earth which implies a diiferent 

 set of physical conditions, and an alteration in the geography of 

 the surrounding country. "We have no means of measuring the 

 period during which this continued to be formed, but it was pro- 

 bably \cry great ; and there was certainly some great change in 

 physical conditions during the deposit of the lower stalagmite, 

 because the fauna of the county (country ?) underwent a strikiug 

 change in the interval. If we add one hundred and fifty thousand 

 years for this pci'iod, we arrive at the sum of half-a-million as 

 representing the years that have probably elapsed since flints of 

 human worknuuishi}) were buried in the lower deposits of Kent's 

 Caveiu. It may be objected that such an estimate is so loose 

 and untrustworthy as to be altogether valueless ; but it may be 

 maintained, on the other hand, that such estimates, if sufliciently 

 multiplied, arc of great value, since they help us to form a defi- 

 nite idea of wliat kind of periods we arc dealing with, and furnish 

 us with a series of hypotheses to be corrected or supported by 

 further observation, and will at last enable us to amve at tlie 

 antiquity of man witliin certain probable limits of error. With- 

 out laying stress on any portion of the above veiy rude estimate, 



