With reference to the accumulation of deposits, whether derived from disintegration of the roof and walls of the cave, introduced by land floods or river inundations or by the residence of man, their rate is of very difficult estimation. Loose stones fallen from the roof, as in the case of Kent's Cave, would give a fair measure of time if we could be sure that the climate had continued uniform, and that there had been no violent earthquakes. Mr. Pengelly has, however, hopelessly given up this kind of evidence. Where, as in the case of many of these caves, land floods and river inundations have entered, these may have been frequent or separated by long intervals of time, and they may have been of great or small amount. Where, for instance, as in one of the Belgian caves, there are six beds of ossiferous mud, but for the fact that five layers of stalagmite separate them we might not have known whether they represent six annual inundations, or floods separated by many centuries from each other. In the case of the Victoria Cave at Settle, Dawkins, reasoning from the accumulation of two feet of detritus over British remains that may be supposed to be 1200 years old, gives a basis which would at the same rate of deposit allow about 5000 years for the date of palaeolithic men; but Prestwich and others, on the basis of stalagmite deposits, claim a vastly higher antiquity for the men who made the implements found in Kent's Hole and Brixham. If we now turn to these stalagmite floors, when we consider that they have been formed by the slow solution of limestone by rain-water charged with carbonic acid, and the dropping of this water on the floor, and when we are told that in Kent's Cavern a marked date shows that the stalagmite has grown at the rate of only one twentieth of an inch since 1688, and that there are two beds of stalagmite, one of which is in some places twelve feet thick, we are impressed with the conviction of a vast antiquity. But when we are told by Dawkins that the rate of deposit in Ingleborough Cave may be estimated at a quarter of an inch per annum, and when we consider that the present rate of deposit in Kent's Hole is probably very different from what it was in the former condition of the country, stalagmite becomes a very unsafe measure of time. With respect again to the accumulation of kitchen-midden stuff in the course of the occupancy of caverns, this proceeds with great rapidity, when caves are steadily occupied and it is not the practice to cleanse out the debris of fires, food, and bedding. Even when the occupation is temporary, a tribe of savages engaged with the preparation of dried meat and pemmican in a very short time produce a considerable heap of bones and other rejectamenta.