240 Prof. Bonney : Penological Notes on the Euphotide 



patches with a slight approach to foliation, though traces of 

 an ophitic structure may sometimes be observed. The struc- 

 ture resembles, though it is less definite and On a coarser 

 scale, that figured on plate xliii. in Mr. Teall's ' British Petro- 

 graphy ' (a gabbro from the Lizard district). Common. 



(5) The typical " euphotide," consisting of white or almost 

 white saussurite, and bright green smaragdite, structure gra- 

 nular to ophitic, texture moderately coarse to very coarse 

 (patches of either mineral up to full 2 inches in diameter). 

 Very common. 



It must not, however, be supposed that these different 

 types can be separated by hard and fast lines. In the same 

 block one variety may pass into another, such as (3) into (5), 

 or even (4) into (5), by the gradual incoming of smaragdite, 

 at first in a u spotty " fashion, and by induration of the 

 felspathic constituent, or a coarse and a fine variety may be 

 associated in a way to which we shall have again to refer. 



How far, then, are these types represented in the ridge ? 

 We struck it on the northern side, near to the western end, 

 where it rises from the snow, and went to the other one along 

 its crest*. On returning, we left the ridge by its southern 

 face. The greater part, so far as we could see it, consists of 

 the hornblendic variety of the gabbro (4), which, however, 

 occasionally loses this schistose structure and becomes nor- 

 mally holocrystalline. Smaragdite occurs only locally. 

 Occasionally also the rock becomes slightly streaked or 

 banded by the incoming of lines of darker, more hornblendic, 

 rock. We met with no evidence here which was conclusive 

 as to the origin of the foliation. The ordinary structure 

 might not unreasonably be claimed as a result of dynamo- 

 metamorphism, but the last-named one seems to require some 

 other explanation. We found a few thin dyke-like masses of 

 a more compact rock, some of which reminded me of that 

 generally fine-grained augitic or hornblendic rock which 

 breaks into, but is intimately associated with, the gabbro at 

 the Lizard. The smaragdite-euphotide occurs, so far as we 

 saw, only at the eastern end of the ridge ; more abundantly, 

 it is my impression, on the southern than on the northern 

 sidef- We observed the normal type (5) and occasionally 

 the one with little smaragdite (3) ; we also noticed that the 



* This consists rather of a pile of separate blocks than of solid rock. 

 As is common in mountainous regions, the tl coping stones" of the wall 

 are more or less displaced. 



t Captain Marshall Hall also found it on the crags at the eastern end, 

 and I have no doubt that it occurs in other parts of the ridge, but in those 

 which we saw it was certainly subordinate to the other variety. 



