142 BRITISH ASSOCIATION, &C. 



hj animals. Mr. Evans then gave an elaborate description of the flint flakes 

 and tools found in these caverns, and referred to the molecular changes 

 vfliich took place in block flints, so as to make them actually soft. — Me. 

 Busk Avas of opinion that the longitudinally split bones had been gnawed by 

 hyffinas, and were probably split by them during the operation. — Mb. Boyd 

 Dawkin referred to the fragment of calcined bone produced by Mr. Pengelly, 

 as evidence that the ancient human occupants of the cave were acquainted 

 with the use of fire. — Me. Pengelly, in reply, wished it to be understood 

 that he only said bones could be split by men in the manner described. He 

 maintained that man had lived in the cavern, as well as the hysena, for he 

 had shown, in previous years, that the hearth, with calcined bones and the 

 tools of man, had been found therein. 



Aetificial Eocking-Stones. — An Expeeiment by W. E. Gkove, F.E.S. 



Some short time ago, during an excursion in Cornwall, my attention 

 was naturally directed to rocking- stones, and those approximations to rocking- 

 stones which are seen in the granite where it is exposed to the action of the 

 heat and cold, air and water. I presume that I need not argue here that 

 rocking- stones are natural results and not superposed on their pedestals, as 

 was once believed, by the hand of man. 



Throughout the greater part of the granite rocks of the west coast of 

 Cornwall, formations are to be seen ai^proaehing in character to rocking- 

 stones, or to discoid piles like the Cheesewring. 



If we suppose a slab of stone of a parallelepiped form lying on another, 

 both having flat surfaces, or in other words such slabs as are formed by 

 fissures in horizontal and perpendicular directions which are common in 

 exposed granite rocks, the attrition and disintegration produced by changes 

 of weather, of temperature, &c., would necessarily act to the greatest extent 

 at the corners and next to that at the edges, because those parts expose 

 respectively the greater surfaces compared with the bulk of the stone. This 

 would tend to round off all the angles, and gradually change the rhomb more 

 or less towards an oblate spheroid. This would account for the Cheesewring, 

 &c. But, then, it may be asked, why should this process gradually work on 

 to a rocking-stone ; in other words, why should the last unworn point, points, 

 or line, be in the line joining the centre of gravity of the upper stone with 

 that of the earth. Such an accident, it may be said, might happen, but the 

 chances are almost infinity to a iinit against it. Not so ; assume the wear- 

 ing away between the slabs ■ to reach a point which is not in the line of 

 centres of gravity, the upper stone would then fall on one side, leaving the 

 unworn point most exposed to climatal and probably to electro-chemical action 

 from the water lying in the angle of the crevice, evaporation being less rapid 

 there than at other parts. This point would then be worn away, and the 

 stone would fall back a little ; then fresh action upon new surfaces, another 

 oscillation, and so on. The effects which I have explained as taking place 

 by steps, would, in fact, take place by insensible pi'ogression. By assuming 



