14 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NovVl^; 



the principal iissures coinciding with lines of small faults averaging 

 about 2 feet in their displacement : in fact, the chalk appears to have 

 been subjected to much lateral pressure ; for, independently of the 

 appearance of the chalk itself, which is occasionally shattered, the 

 flints near to or in the fissures are fractured, and the sides of the 

 fissures present in some places a striated appearance, as if they had 

 been rubbed against each other in a vertical direction, and coincident 

 with the displacement of the rock. The fissures vary in size, and 

 their upper parts frequently present an irregular funnel-shaped 

 structure. 



The movements above alluded to were probably due to that general 

 disturbance which has affected the whole area, and has been partly 

 described by the Rev. H. M. De la Condamine, in his paper '* On the 

 Tertiary Strata and their dislocations in the neighbourhood of Black- 

 heath*." 



The derangements of the chalk must have taken place posteriorly to 

 the deposition of the superior tertiary strata ; for, although the upper 

 surface of the chalk presents an undulating appearance, and the layer 

 of green-coated flints lying above may be said to repose on a tolerably 

 even surface, yet indications of slight disturbance may be observed in 

 this stratum, parallel to the lines of faults, and which could not, of 

 course, be readily observed in the sand above. 



With this band of flints, generally encrusted with silicate of iron, 

 are associated thin seams of clay, clayey sand, and impure fuller's 

 earth ; and these are overlaid by the well-known " ash-coloured sand " 

 (Thanet Sand) so characteristic of this portion of the series. 



No trace of allophane has been observed in the ash-coloured sand, 

 nor does it form a continuous layer on the surface of the chalk. 



The greatest quantity is met with near to, and in, the funnel- 

 shaped cavities, and also lining some of the fissures previously men- 

 tioned. 



It occurs in different ways; sometimes formir^ layers following 

 the irregularities of the cavities ; sometimes intermixed with the 

 ochreous sand and clay, and coating the flints (which have been 

 previously abraded) with a more or less thickened crust ; at other 

 times it I'nay be observed formed into large concretions, which, upon 

 drying, present a concentric arrangement. The allophane is con- 

 tinued downwards, -lining the fissures (which are irregular in width) 

 on each side, in the manner of the gangue of a vein, and even filling 

 them up, and encrusting any fragment of chalk-flint or broken flints 

 that existed in the fissure. The allophane is found in the fissures to 

 the present depth of the workings in the chalk (about 15 to 20 feet), 

 and is probably continued further downwards. 



One of the principal veins containing the allophane occurred in the 

 middle of the pit, and is now worked out, traces of it remaining on 

 the north and south sides ; the chalk on each side was rotten, pre- 

 senting hues of irregular vertical cleavage, probably owing to the 

 lateral pressure it had undergone. On the south side the fissured 

 chalk, about 8 feet wide, was traversed by small veins of allophane, 

 * Quart. Journ. Geol. Soc. \?ol. vi. p. 441 ; ibid. vol. viii. p. 193. 



