In addition to the proofs, already adduced, of the solubility of 

 silex in water, we may notice the circumstance of its having been 

 found, in the proportion of 14 grains to 20 ounces, of the water 

 collected in the cavities of basaltic columns. Its having circulated 

 in the vessels of the animal body, and having been separated by 

 the vessels of secretory organs ; and thus forming, though rarely, a 

 part of the human urinary calculus, may also be regarded as evi- 

 dence of some weight. But its presence in different plants affords 

 still more powerful proof of its solubility, since we cannot conceive 

 its absorption, its transportation through the substance, and, lastly, 

 its deposition in certain parts of plants, but in a state of actual 

 solution in the* water, with which the plant is nourished. Its pre- 

 sence in the ashes of plants is well known. Rumphius relates *, 

 that in the island of Celebes, near Macassar, stones are frequently 

 found, naturally formed in the wood, and fruits of different trees: 

 and that they are worn by the natives, being supposed by them 

 to possess extraordinary powers; particularly that of defending 

 them from the injuries of any weapon. These, however, will not, 

 alone, afford us any considerable support ; since, although the 

 learned author describes them as flint-like stones, he mentions that 

 they do not give sparks, and that they effervesce on being placed 

 in an acid liquor. Mr. Macie has, however, found a pebble in the 

 joint of a Bamboo cane, which was so hard as to allow it to cut 

 glassf . Mr. Davy has ascertained, most clearly, that flint enters 

 into the composition of the epidermis of bonnet-cane, and indeed, 

 of all cane of this kind. He found that when pieces of this kind 

 of cane were rubbed together, strong sparks of white light were 

 produced ; and that, when forcibly struck together, the sparks were 

 as vivid as those from a gun-lock. The cause of this was ascer- 

 tained beyond all doubt, by his finding that 22 grains of the epi- 



* D'Amboinsche Rariteit-Kamer. Ill Bock. LXVIII Hoofsdeel. 

 t Philosophical Transactions, 1791, p. 385 



