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The Twenty-Ninth General Meeting. 



their kindred. I remember an old answer to the question, "What 

 is flint ?" was one a Roman might have given. " Why it's silex." 

 The mineralogist will give a fuller bnt still an incomplete answer, 

 for the biologist will have yet to add an important contribution to 

 it. The mineralogist will tell you that flint is a mineral similar in 

 composition to quartz crystal and to chalcedony, and therefore also 

 to agate, onyx, sard, chert, jasper, and a tribe of substances, beautiful, 

 many of them, and wonderfully varied in aspect and colour. He 

 will tell you that these minerals have a common composition, or, 

 rather, have for their predominating ingredient the substance called 

 silica, or silicon di-oxide, which is the oxide of an element, silicon, 

 and which further has the nature of an acid, and forms when com- 

 bined with bases a series of compounds or " salts " termed silicates. 

 And he will tell you that the crust of the world is, to a very largely 

 predominating amount, composed of the classes of rocks, the 

 ingredients of which are silicates or silica, or both : i.e., that 

 most rocks are either mixtures of different silicates, or of such 

 silicates with an admixture of quartz, the crystallised variety of 

 silica ; or again they may consist of sandstone, which is little else 

 than silica, generally as quartz, in the form of a compacted sand. 



Hollows in certain of these rocks that have at one time, under 

 the influence of subterranean heat, flowed as lavas, are found to 

 contain the uncrystallised form of silica known as chalcedony in a 

 variety of mineral forms, such as agate, jasper, &c. But chalcedony 

 is found in mines and elsewhere under conditions where no fusion 

 and no heat has ever come near the place in which the mineral 

 occurs. 



It may be seen, for instance, frequently coating the hollows of 

 the flints you may pick up in Pewsey Yale, or at Folkestone, and 

 other places, covering them with a beautiful botryoidal or smooth 

 grape-like surface, with often a sort of bloom on it like a plum. 

 Here no subterranean heat has approached the beds in which the 

 flints have lain. 



Indeed the facts regarding properties of chalcedony and its forma- 

 tion in Nature all point to the conclusion that it has been deposited 

 not by the agency of heat, but from solution in water, generally as 



