In the Pipernoid Tuff of the Campania. . 313 



has been formed at the expense of the calcite of the limestone. 

 This arragouite would seem to indicate some slight warmth to 

 have existed for its formation, but whether of original volcanic heat 

 of the tuff itself or dependent upon heat liberated in the chemical 

 decomposition going on, it is not easy to determine. 



The quantity of fluorine must have been very considerable, because 

 the amount of fluorides formed constitute the major part of the 

 products of metamorphism. 



The whole of these changes, therefore, was due to some fluorine 

 compound in the original volcanic material, which A. Scacchi shows 

 would most likely be hydro-fluosilicic acid. 



Fluorine and minute quantities of fluorides have often been found 

 in volcanic emanations, but the quantity that must have accompanied 

 the dust and scoria of the eruptions to which we owe the pipernoid 

 tuff was exceptionally gi-eat. Where these and other constituents of 

 the tuff have been reacted upon slowly with calcite in any form, 

 either organic or inorganic, certain minerals have resulted which 

 are supposed to require very high temperatures, and in some cases 

 high pressures, for their genesis. Of course the mode of formation 

 of hornblende under such conditions is of interest in considering 

 the case where this mineral occupies vesicles or fissures in a cooling 

 lava, but does not in any way militate against the fact of its 

 individualization from a vitreous base being still regarded as 

 indicative of high temperature and pressure.^ 



Finally this is one more confirmation of the fact of the great 

 importance we must attach to fluorine as a mineralizing agent. 



I must thank my friend and colleague Prof. P. Franco for kindly 

 clearing up by careful measurements some doubts about the minerals 

 epigenized upon the bone. 



Minerals Formed on the Fossil Bones of the Tufa of Faiano 



near nocera. 



It is a known fact that in the volcanic tuffs of the Campania 

 bones of ruminants occur with minerals superposed on their surfaces 

 and in their cavities. A. Scacchi^ described a tibia found by and 

 contained in the valuable collection of Prof. Johnston-Lavis as well 

 as a vertebra in the collection of the University Museum in Naples. 

 On these bones he recognized hematite and amphibole. A. Scacchi 

 adds that there are minute brownish-yellow crystals of indetermin- 

 able form, but which, under the microscope, appeared by the 

 distribution of some of the faces to be rectangular ; he likewise 

 mentions some thin white crystals, that are not mica. 



Dr. Johnston-Lavis has courteously allowed me to examine the 

 specimen described by Scacchi. I have been able to recognize on 

 it a pyroxene (augite), mica, and I have determined the form of the 

 amphibole crystals, which was not done by Scacchi. 



^ H. J. Johnston-Lavis, "Relationship of the Structure of Igneous Rocks to the 

 Conditions of their Formation," Scientiiic Proc. Royal Dublin Soc, vol. v, n.s., 

 pp. 112-156; also Q.J.G.S., vol. xli, pp. 103-106. 



- A. Scacchi, " Sulle ossa fossile trovate nel tufo dei viilcani fluoriferi della 

 Campania," Atti dell' Ace. delle Scienze di Napoli 1888, p. 6 ; and also "La Regione 

 vulcanica fluorifera della Campania," Mem. del R. Comitato Geoligico Ital., 2nd 

 ediz., Fii-enze, 1890, p. 34. 



