830 Reports and Proceedings — 



arragohite in sucli a way as to give rise to a product containing 

 42 per cent, of carbonate of magnesium. Below 60° C. the action 

 is very slight, but between 60° and 91° there appears to be for each 

 temperature a certain maximum amount of replacement possible. 

 When the solution is not concentrated with common salt the 

 sulphate of magnesium acts much less energetically. The powder 

 of Iceland spar, unlike that of arragonite, is scarcely acted upon at 

 all under similar circumstances. The powder of corals, on the 

 other hand, is affected in the same way as that of arragonite. Thus 

 Madrepora humilis from the island of St. Thomas yielded a product 

 containing 41-9 per cent, of carbonate of magnesium after treatment 

 for 47 hours at 90° C. 



. The author shows that the product formed in his experiments is 

 not dolomite, but a mixture of the two carbonates. He considers, 

 however, that true dolomite may be formed from such a mixture by 

 secondary processes. 



The author finally discusses the question as to whether the 

 conditions of his experiments can be realised in nature on a large, 

 scale. Chloride of sodium and sulphate of magnesium are both 

 present in sea-water, which may be concentrated in the closed 

 lagoons of certain atolls. The debris of corals composed of 

 arragonite is present, and the rays of the sun in tropical regions 

 are capable of raising the temperature of such closed basins far 

 above 60° C. He concludes, therefore, that " dolomite is formed by 

 the action of sea-water, concentrated in closed basins and heated 

 by the solar rays, on the arragonite deposited by organisms, in such 

 a way that a mixture of the carbonates of calcium and magnesium 

 is first produced, and subsequently converted into dolomite." 



J. J. H. T. . 



lE^EJi^OK-Ts j!^i<riD :PI^OG:H;:BIDI^5^a-s. 



Geological Society of London. 



I._May 22, 1895,— Dr. Henry Woodward, F,R,S., President, in 

 the Chair. The following communications were read : — 



1. "On a Human Skull and Limb-bones found in the Paleeolithic 

 Terrace-Gravels at Galley Hill, Kent." By E. T. Newton, Esq., 

 E.R.S., F,G,S. 



A human skull with lower jaw and parts of the limb-bones were 

 obtained by Mr. R. Elliott from the high-terrace gravels at Galley 

 Hill, in which numerous PalfBolithic implements have been found. 



The skull is extremely long and narrow, its breadth-index being 

 about 64; it is hyperdolichocephalic ; it is likewise much depressed, 

 liaving a height-index of about 67. The small extent of the cranium 

 in both height and width shows that it has undergone little or no 

 post-mortem compression, although it has become somewhat twisted 

 in drying. The snpraciliary ridges are large, the forehead somewhat 

 receding, the probole prominent, and the occiput flattened below. 

 All the chief sutures are obliterated. Three lower molars and two 



