59 



raised till they melt, the alloy is reformed. This is an interesting 

 example of a molecular change in a solid form. — S.K.N.H.S., Feh. 2\st, 

 1889. 



Flint Implement. — On the occasion of Mr. Dowker's paper, entitled 

 " Thoughts in a Gravel Pit ", a Neolithic flint weapon was exhibited, 

 which had recently been found when excavating for the foundations of 

 an ordnance store near the Priory Station, Dover. 



This object, now in the possession of Colonel Corrie-Walker, R.E., 

 was found on the surface of the chalk under the rainwash of brick earth, 

 amounting to about 3 feet 6 inches, and about 18 inches of vegetable soil. 

 It was of grey mottled flint like the tabular flint of Pegwell Bay, about 

 8 inches long and 2J at the broadest end, which was ground smooth. 



D. F. C. and K. H. S., Dec. l^h, 1889. 



Singular Pebble. — Mr. Sydney Webb exhibited an oval pebble from 

 the beach at South wold, with the view of shewing that silica in its 

 various forms of flint, &c., must have been once in a mud-like condition. 

 The exterior of the pebble, which has been polished over a portion of its 

 surface, without cutting, is transparent chalcedony ; but the remainder 

 is unpolished, of a dull yellow color. Viewed from above the chalcedony 

 (as a sheet of glass) shows this yellow portion to have contracted whilst 

 soft ; by this action broad cracks in its substance were formed, which 

 later on were flUed in and covered over by the superincumbent trans- 

 lucent material, with a very pleasing effect. — D.F.C. 



Mr. Dowker supplements the description thus: — The pebble is the 

 result of metamorphism, whereby a septarian concretion, which had, 

 perhaps, the cracks filled originally with calc-spar now shews them 

 covered by chalcedony. It is well known that in the " London Clay " 

 concretions of nodular clay and limestone are abundant, but it is im- 

 possible to determine from what bed this specimen was derived in the first 

 instance. Biller's spar and calc-spar are often replaced by silica ; indeed, 

 Bischof states that l5iller's spar acts as the precipitate for silica. But the 

 alteration of a mineral is an extremely slow process. It is accomplished 

 in the wet way by water that holds certain substances in solution being 

 brought into contact with the mineral, and the pseudomorphic process 

 may be imagined to consist either in direct conversion of minute particles 

 of the original mineral into the uew substance, or in a series of inter- 

 mediate changes, the results of which are minerals siiccessively more 

 distinct from the original in composition, and nearer to the final product. 

 Crystalline and amorphous quartz are associated in petrifactions as well 

 as in amethyst druses, the former occupying the interior, the latter the 

 exterior. In many belemnites quartz and heavy spar are found as 

 petrifying materials, so that the upper part of the sheath consists of 

 quaitz, and the lower part of sulphate of baryta. In this specimen 



