490 Queries and Answers. 



of density in the mass, which could not be increased without 

 producing, as in granite, fissures running through it : the par- 

 ticles may be supposed to be held in a certain degree of ten- 

 sion, and there may be a tendency to what the French call 

 assaissement (I do not know the English term), which is, 

 nevertheless, resisted by the stone en masse ; and a quantity of 

 water may likewise be held, not in a state of chemical combi- 

 nation, but in one of close mixture with the rock. On being 

 broken or quarried, the assaissement may take place, the par- 

 ticles of stone may draw closer together, the attraction become 

 stronger ; and, on exposure to the air, the water, however 

 intimately combined, will, in a process of years, be driven off, 

 occasioning the consolidation of the calcareous, and the near 

 approach of the siliceous, particles, and a consequent gradual 

 induration of the whole body of the stone. I offer this sup- 

 position with all diffidence : there may be many other causes, 

 which cannot be developed until proper experiments have 

 been made. It would be interesting to ascertain the relative 

 hardness of different specimens of sandstone, taken from dif- 

 ferent depths in a bed, the surface of which was exposed to 

 the air, as of specimens exposed to the air for different lengths 

 of time. — J. R. Heme Hill, July 25. 1836. 



Mr. P. Hunter's Queries on Geologic Subjects in p. 380, 38 1. 

 I give the best solution of them that occurs to me at present, 

 as follows : — 



" Can any of your Correspondents recommend something more 

 efficient to prevent the Decomposition of these interesting Fossils ? n 

 (p. 380-1.) — I have found strong transparent varnish a good 

 preservative for fossil bones found in clay deposits ; but I do 

 not know that there was very much pyrites in those fossils so 

 preserved, although it is well known to be an abundant mineral 

 in all clay deposits. As pyrites decomposes most rapidly 

 when atmospheric air has free admission into its pores, the 

 stopping up of those pores is most essentially necessary ; and, 

 on this ground, I think that, if we were to add to the washing 

 with turpentine and lamp oil, recommended by Mr. Hill, the 

 giving of the fossils, after allowing them time to dry, a 

 dressing of dissolved isinglass, it would be the best mode 

 to preserve them from decay. I have known the tusk of an 

 elephant, 7 feet 8 inches long, and 8 inches in diameter at the 

 base, which was found fossilised in the London clay at Walton, 

 in Essex, well preserved by simply a coat of varnish : this 

 tusk was, when found, in a forward state of decomposition. 



" What is done with the immense Quantity of Pyrites col- 

 lected on the Beach at Sheppey, which is shipped off to London, 

 &c. (p. 381.) — Iron pyrites was formerly collected on the 



