J". W. Judd — On Volcanos, 207 



and Des Cloiseaux as a hornblende, is now pretty generally accepted 

 as augite), constitute the whole mass. Sometimes the augite is 

 replaced by diallage or hypersthene, and occasionally the felspathic 

 ingredient almost wholly disappears, and we have an augite-, 

 diallage-, or hypersthene-rock. 



In illustration of the ultimate composition of the varieties of the 

 celebrated Monzonite-rock, we may cite the following analyses : — 





(1) 



(2) 



(3) 



SUica , 



.... 58-05 



50-80 



38-18 



Alumina 



... 17-71 



16-20 



10-06 



Peroxide of Iron 



— 



— 



17-50 



Protoxide of Iron 



... 8-29 



14-37 



9-47 



Lime 



... 5-81 



10-00 



11-84 



Magnesia 



... 2-07 



3-53 



9-72 



Potash 



... 3-24 



•••■ 1 3-90 



1-38 



Soda 



... 2-98 



0-52 



Water 



... 1-34 

 99-49 



1-20 



1-26 



Totals 



100-00 



99-93 



(1) is tlie analysis of a typical Monzoni-syenite (Augite-syenite of vom Eath) by 

 Kjerulf. The specimen was obtained from the Margola near Predazzo. 



(2) and (3) are analyses of more basic rocks (diabase or pyroxene-Monzonite) of 



the Canzacoli near Predazzo. (2) is an analysis by Delesse ; (3) by Konya, 

 as given by Tschermak. 



The " Tourmaline -granite " is, like the Monzonite, a rock of truly 

 granitic structure, although now universally regarded as of volcanic 

 origin. It is a well-marked granite of a red colour made up of 

 orthoclase of a more or less deep pink tint, white or greenish plagio- 

 clase, grey quartz and biotite. But in addition to these minerals 

 we find, and generally in association with the quartz, considerable 

 quantities of tourmaline, forming masses of radiating crystals some- 

 times of large size. The drusy cavities, which sometimes occur in 

 the rock, frequently contain various beautifully crystallized minerals. 



The following analysis of the Tourmaline -granite of the Mulatto 

 near Predazzo, which was made by Kjerulf, will serve to illustrate 

 its ultimate composition : — 



Silica 70-73 



Alumina 14-16 



Peroxide of Iron 3-59 



Lime 1-03 



Magnesia 0-66 



Potash 5-37 



Soda 2-54 



Loss 1-10 



Total 99-24 



Tschermak regards this rock as essentially composed of 30 per 

 cent, of Quartz, 32 of Orthoclase, 27 of Oligoclase, and 10 of 

 Tourmaline. 



The next rocks, taken in the order of their appearance, are those 

 which von Buch and the earlier writers spoke of as black-porphyries 

 and basalts ; they are now classed as Melaphyres, Augite-porphj^ies 

 and Uralite -porphyries. The so-called Melaphyres consist princi- 

 pally of plagioclase felspar with occasionally a little orthoclase, augite, 



