Geological Society. 359 



In the first of these two cases the successive losses of 

 energy are shown by a series of plus numbers diminishino- in 

 value down to the combining proportion ; in the second one 

 the losses are shown by a series of minus numbers increasing 

 in value towards the combining proportion. In each case the 

 relative amount of energy decreases with each successive pro- 

 portion of substance added until the combining proportion is 

 attained, and then commences to increase. 



XL III. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 282.] 



February 6, 1889.— W. T. Blanford, LL.D., F.E.S., President, 

 in the Chair. 



nnHE following communication was read : — 

 -^ 1. " On the Occurrence of Palaeolithic Flint Implements in 

 the neighbourhood of Ightham, Kent, their Distribution and pro- 

 bable Age." By Joseph Prestwich, D.C.L., F.P.S., F.G.S. 



The author stated that Mr. Harrison of Ightham has discovered 

 over 400 palaeoHthic implements lying on the surface at various 

 heights and over a wide area around Ightham. A description of the 

 physiography of the district and of the distribution of the various 

 gravels and drifts was given, and in the absence of fossils, attention 

 was called to the different levels at which the deposits occurred, and 

 to their physical features and characters. Besides the river-gravels, 

 two groups of unclassed gravels were described, one occupying a 

 low level, and the other levels higher than that to which the river- 

 drifts reach ; the latter is of varied composition. 



In the case of the Shode valley, only beds below the contour-level 

 of 350 feet in its upper part, and of 300 feet or less in its lower 

 part can be referred to the former action of the Shode, and those 

 above this belong to a high-level drift of uncertain age. The com- 

 position of the various gravels was described in detail. 



The implements are found on the surface of the land at all levels 

 up to 600 feet, and Mr. Harrison has discovered them at 40 localities 

 in the hydrographical basins of the Shode, the Darent, the Ley- 

 bourne stream, and in part of the Thames basin. Two groups of 

 implements extend far beyond tbe limits assigned to the river-drifts 

 formed since the present hydrographical basins were established, and 

 must be accounted for by some other means than those in connexion 

 with the former regime of the existing streams. A description of 

 the general characters and variations observable in the implements 

 was given. 



