532 Dr. T. Sterry Hunt — rOn Italian Geology. 



same time that '' the work of Gastaldi, interrupted hy his death in 

 1878, was unfortunately left incomplete." This statement was not 

 quite exact in one particular, since he survived till January 5, 1879, 

 when there passed away, universally honoured and beloved, one 

 who brought to the study of geologj'', with a spirit of complete 

 devotion, a rare genius and a breadth of view which will assure him 

 a first place among the geologists of our time. 



In the chapter above mentioned the writer proceeded to consider 

 the history of the so-called Tertiary serpentines of Monte Ferrato in 

 Prato (Tuscany), and those of parts of the Ligurian Apennines 

 which he had personally examined, and, in opposition to the opinion 

 of most Italian geologists, and some others who have studied them, 

 maintained that they were really but portions of the ancient pietre 

 verdi zone, identical with that of the Alps, underlying, in the regions 

 in question, the beds of Eocene age ; which latter, by subsequent 

 terrestrial movements, have been disturbed, broken and even inverted, 

 so as to seem to pass beneath the serpentinic rocks. The indigenous 

 and neptunian character of serpentine, maintained on stratigraphical 

 evidence in North America by E. Emmons, by Logan, and by the 

 present writer, was not only held by Gastaldi and Delesse, but is 

 maintained by Stapff, by Lotti, and by Dieulefait. The hypothesis 

 of a plutonic origin has moreover been so much modified by recent 

 Italian geologists, as Taramelli, Capacci, Issel, and Mazzuoli, that 

 instead of supposing them to have been erupted like basalts, they 

 now conceive that serpentines, and the associated rocks of the 

 ophiolitic group, were formed by submarine eruptions, in Tertiary 

 time, of magnesian and feldspathic muds, of unexplained origin but 

 of no very elevated temperature ; which subsequently consolidated 

 and crystallized into euphotide, diorite, and serpentine, with their 

 associated feldspars, enstatite, chrysolite, and other minerals. 



In the change of chrysolite into serpentine, as I have elsewhere 

 shown, " one hundred parts by volume of the former species, with 

 a specific gravity of 3-33, if converted into serpentine of specific 

 gravity 2-50, without change in its content of silica, must lose one- 

 eighth of its weight of magnesia, and acquire the same amount of 

 water instead, while at the same time its volume will be augmented 

 one-third, or to one hundred and thirty-three parts." That such a 

 change takes place in some instances, probably through the action of 

 carbonated waters removing a portion of magnesia from chrysolite, 

 and leaving behind the more stable hydrated and colloid silicate, 

 serpentine, is evident. Until, however, the precise conditions under 

 which this may take place are better understood, we cannot explain 

 why in some cases chrysolite is exempt from such change. I have 

 long since described in the vicinity of Montreal, in Canada, cutting the 

 limestones and pyroschists of the Ordovician series, great masses of 

 a granitoid chrysolitic dolerite, itself of Palseozoic age, in which the 

 chrysolite, in large crystals, often predominates, and is still unchanged, 

 hard, and anhydrous. The assumption, lightly made by some plutonists^ 

 that chrysolite is always of plutonic origin, and serpentine always 

 a product of epigenesis, rests upon a slender foundation, and is in 



