312 Prof. Johnston- La vis — Formation of Minerals — 



same bones of different animals. The tibia is one of the densest 

 bones of the body, and the part analysed by Scacchi was the shaft 

 portion and therefore the densest part ot that bone. Still, it will be 

 seen that the calcic phosphate is very high — over 93 per cent, of the 

 inorganic constituents : whether this be due to a conversion of some 

 of the original calcic carbonate into phosphate is not easy to say. 

 What, however, is strikingly evident is the conversion of a large 

 part of the calcic carbonate into calcic fluoride so as to constitute 

 over 6 per cent. Fluorine does occur in bones, but in very minute 

 proportions. If we consider the other 6 or 7 per cent, of carbonate 

 to have become phosphate we could then explain the high proportion 

 of this latter compound in Scacchi's analysis. 



The organic matter in the Faiano specimen amounts to 5'48 per 

 cent., and Scacchi, in making his analysis, was struck by the fact 

 that in heating the creamy-white bone it blackened and gave off an 

 odour of burnt horn. He did not appreciate the valuable bearing of 

 such a fact on mineral genesis, for it proves incontrovertibly that 

 the minerals associated with this bone could not have been produced 

 at a temperature sufficiently high to even discolour it, much less to 

 carbonize its organic matter. Not only this, it likewise shows that 

 the other minerals formed at the expense of the limestone fragments 

 in its immediate neighbourhood must likewise have taken place at 

 a low temperature. 



Dried bones afford about 11'40 per cent, of nitrogeneous organic 

 matter and 15-75 per cent, of fat. ]f we suppose all the fat to have 

 disappeared we even then find the quantity of ossein far below the 

 normal. This could hardly be more than we should expect — it is 

 astonishing rather that such a quantity of organic matter has 

 remained, and its existence points to no very great antiquity of 

 the tuff, which certainly is anterior to the last 660 metres in height 

 of Monte Somma, previous to its great prehistoric truncation, which 

 truncation must be anterior to the last 3000 years. The vertebrae 

 obtained by Scacchi from the neighbouring quarry had lost their 

 organic matter — a state of things to be expected in such porous 

 spongy bones, but they likewise had all their calcic carbonate 

 converted into fluorite. 



In the Faiano and Fossa Lupara quarries, numbers of fragments 

 of limestone have been enveloped in the tuff and have undergone most 

 marked changes. Ail the blocks up to the size of a cocoa-nut have 

 been entirely converted into a mass of beautiful brown mica crystals, 

 which form a shell having the original shape of the enclosure. 

 Within this shell is a hollow space with elegant groups of hyaline 

 globules or radiating bunches of fluorite associated with delicate 

 fibres and needles of nocerite. Besides the mica are crystals of 

 augite, hornblende, and a mineral of the nepheline group, but very 

 impure from enclosures. 



Where large blocks of limestone occur, they are in some cases 

 covered with a solidified froth of fluorite, or their surfaces are 

 converted for the depth of several centimetres into mixture of the 

 silicates and fluorides above mentioned, whilst farther in arragonite 



