244 Prof. Bonney : Penological Notes on the Euphotide 



it is pseudobrookite*. Characteristic microliths of rutile are 

 occasionally present. 



I have thought it needless to examine microscopically one 

 of the specimens where the pyroxenic constituent is diallage, 

 for macroscopically it is an ordinary gabbro, with the felspar 

 considerably and the diallage slightly altered. I cannot 

 detect any olivine, but this mineral occurs in the gabbro of 

 Mont Colon f. Here the pyroxene changes into a rich green 

 hornblende, as it also does (though, if my memory be correct, 

 the colour is a little paler) in the gabbro mass on the west 

 flank of the Matterhorn. I do not remember to have seen 

 smaragdite at either of these localities ; probably its occur- 

 rence in the Saasthal mass is due to some slight accidental 

 difference in chemical composition %. 



Among the boulders was one resembling a dark greenstone 

 in which were scattered a few fairly conspicuous crystals of 

 smaragdite. Under the microscope it appears to be composed 

 of saussurite and various pyroxenic and hornblendic consti- 

 tuents, much as above described (without glaucophane), but 

 very confusedly mingled ; the only well-defined mineral being 

 small garnets with " dusty " centres and generally rounded 

 outlines. It is quite possible that the constituents may have 

 been crushed up together ; but, if so, the last-named either 

 have escaped or are later in date. There are also a few well- 

 formed flakes of white mica, and sometimes (as observed by 

 Dr. Sterry Hunt) a small quantity of talc. 



It follows from what is said above that most of the con- 

 stituents in these euphotides are of secondary origin ; and the 

 rock is the result of mineral change in a coarsely crystalline 

 gabbro which originally consisted mainly of a plagioclase fel- 

 spar, such as labradorite, and a diallage (or possibly augite). 

 It is difficult to determine whether the garnets are original 

 constituents of the rock or not, for the evidence appears to 

 me rather conflicting ; this may be due to the fact that the 

 Alps have been subject to disturbance at more than one epoch ; 

 perhaps it is on the whole more probable that they also are 

 secondary. 



* This mineral is frequent in the glaucophane eclogites. It is that 

 noticed by myself, as probably impure sphene or rutile, in the rock from 

 the Val d'Aosta (Min. Mag. vol. vii. p. 3), and by Mr. Eutley, Quart. 

 JourD. Geol. Soc. vol. xlv. p. 61. 



t See the author, " On some Specimens of Gabbro from the Penniue 

 Alps," Min. Mag. vol. ii. p. 5. 



X Dr. Sterry Hunt (' Contributions to the History of Euphotide,' &c.) 

 found in the Saasthal smaragdite -61 of Cr 2 3 , with traces of nickel and 

 even of cobalt. This may be the cause of the peculiar colour. 



