THE SOUTHERN PORTION OF THE WEALDEN AREA. 



651 



coarse-grained granite, with an abundance of pink and white 

 felspar, and small grains of quartz. Black mica is also present. 

 Although the rock is much decomposed, I prepared a thin slice for 

 microscopic examination. In this the felspar is seen to predomi- 

 nate largely and is almost wholly kaolinized, scarcely any of it 

 retaining the depolarizing power. Iron stains are common along 

 the edges and cleavage -planes of the crystals. The quartz is in 

 irregular grains, and sometimes discoloured by decomposition-pro- 

 ducts : the grains are generally cloudy, owing to the presence of 

 innumerable minute fluid- or gas-cavities. The mica is biotite, very 

 dark and strongly dichroic. Hornblende does not appear to occur, 

 but some opaque patches of magnetite are to be seen. The section 

 bears a strong resemblance to a specimen of Peterhead granite in 

 my cabinet. 



Until the conveyance of this boulder to its position on the Chalk 

 escarpment by natural transport is confirmed by the discovery of 

 other blocks, it will be better not to venture upon any theory as to 

 its origin, especially as the presence of erratics in such a position 

 would necessitate a modification of accepted views respecting the 

 physical condition of the south of England during the Glacial 

 epoch. 



General Conclusions. — Although it is clear in many cases that the 

 gravels just described bear a close relation to the present drainage- 

 channels, and old river-beds are easily to be recognized at various 

 elevations above the present water-level, yet there are many 

 difficulties to be encountered when it is endeavoured to explain the 

 origin of the beds of angular drift which lie either upon the main 

 watersheds or upon the higher contours far removed from existing 

 rivers. Sir H. Murchison maintained that all the beds of angular 

 drift within the Wealden area, irrespective alike of their position 

 with regard to the river-valleys, their composition, or the evident 

 traces of stratification which many of them reveal, are the results 

 of an agency of vast intensity," of a former powerful but transient 

 current, which " denuded the surface of the bare rocks in many 

 parts, and at the same time distributed broken materials along a 

 zone of limited width," especially where the higher ridges arrested 

 the progress of the current *. In support of this theory he dwells 

 particularly upon the want of stratification in the drifts of this 

 area, and also upon the fact that in the more eastern portions the 

 stones are more waterworn, and finally give place to beds of loam 

 without any admixture of flints. Mr. Martin supported this view 

 with the statement that the Weald valley looks like a great water- 

 channel after a flood — some parts being clean denuded, others loaded 

 with drift t. Prof. Prestwich in 1851 agreed with Murchison in 

 advocating the sudden, tumultuous and rapid accumulation of the 

 angular drift, and Mr. Hopkins, in 1852, expressed similar views +. 



* Quart. Journ. Geol. Soc. vol. vii. p. 349. 



t ' Geol. Mem. of Part of W. Sussex,' p. 84 ; and ' Phil. Mag.' ser. 4, vol. vii. 

 p. 116. 



| Quart. Journ. Geol. Soc. vol. viii. p. xliv. 



2t 2 



