252 R. H. Rastall — Minerals of Barrington Bone-bed. 



reason for believing that alterations in the force of gravity are even 

 now going on at Dehra Dun in India, which would indicate internal 

 movements of mass incompatible with solidity.^ 



Colonel Burrard's theory, of a rift in the sub-crust along the area of 

 low density skirting tlie mountain range, will no doubt receive the 

 consideration which the high position of its author demands for it; 

 but it is obvious that there are difficulties. He appears to believe 

 that the sub-crust beneath the mountains contracted upon itself, and 

 in being shortened laterally became thickened vertically, and rose up 

 into a mountain range, leaving a rift where it parted from the adjacent 

 sub-crust. If it was in a state of tension, it is conceivable that a rift 

 might have been formed, and that it might have contracted upon 

 itself until the tension was relieved. During this part of the process 

 it would have decreased in volume and become more dense. Then it 

 seems to be supposed that the process of lateral contraction continued, 

 and, contrary to what might be expected, it became less dense. 

 A decrease of mass below corresponded to the protrusion of the 

 mountains above. The material remaining below thus became less 

 dense than the mountains which it pushed up, and that in spite of 

 the pressure. Thus partial isostacy would result. These movements 

 being supposed to have gone on in a sub-crust, any rift formed by 

 them would appear to have been more likely to open from below, 

 and to have been filled with heavy material rather than with 

 sediment from the surface. Eifts have been abundantly formed 

 among the older rocks, but they are never empty, but filled with 

 some intrusive material or mineral veins, usually of a denser character 

 than the country rock. An empty rift would be an anomaly. 



In any theory of a mountain range allowance must be made for the 

 enormous amount of material wliich has been denuded from it ; in 

 the case of the Himalayas, the Sewalik range, the alluvium of all the 

 Indo-Gangetic plain, besides what has been carried out to sea by 

 rivers. Elevation in compensation of this waste is continually going 

 on, and it is probable that it is this which is the cause of the 

 frequent earthquakes that occur in the district. 



IV. — The Minerals of tue Bakrington Bone-bed. 

 By E. H. Eastall, M,A., F.G.S. 



OKE of the most important and most interesting features of the 

 geology of the Cambridge district is the deposit at Barrington, 

 so widely known for its richness in mammalian remains. This 

 bone-bed has been described many times, and the literature is large. 

 Most of the descriptions, however, confine themselves chiefly to the 

 organic contents, mentioning briefly the character of the larger stones 

 and pebbles, and saying little or nothing about the nature of the finer 

 matrix in which these are embedded. 



The author has been for some time past engaged in the study of 

 the mineralogical composition of the sands and gravels of Pleistocene 



^ See Colonel Burrard's paper, Phil. Trans., ser. A, vol. ccv, 1905. Also 

 Nature, vol. xci, p. 143, 1905. 



