J. J. Harris Teall — The Lizard Gabbros. 487 



appearance. In the neighbourhood of the village the veins and 

 dykes of gabbro are often foliated, and every transition may be 

 observed from massive gabbro to gabbro-schist. At Karakclews 

 Headland foliation has been developed in a most striking manner, 

 and affects, with a few local exceptions, the entire mass, which is 

 more than a hundred yards in width. The general strike of the 

 foliation is approximately N.W. and S.E., but there is no absolute 

 constancy in the direction ; slight deviations occur sometimes on 

 the one side and sometimes on the other. One important feature in 

 the Karakclews mass is the distinctly banded character of certain 

 portions, particularly those near the southern junction with the 

 serpentine. Light and dark bands several inches in thickness 

 alternate with each other, and with the ordinary fiaser- and augen- 

 gabbro, so that the mass as a whole simulates a stratified series. The 

 small dykes of gabbro in the serpentine near • Karakclews are often 

 foliated, and not seldom one may see the transition from massive 

 gabbro to gabbro-schist taking place in the space of a few inches. 



Another locality where foliation is well developed is north of 

 Pen Voose near Landewednack. The main mass of gabbro is 

 separated from serpentine and other rocks on the north by a well- 

 marked fault-plane. In the immediate neighbourhood of this plane 

 the gabbro is foliated, and passes into a fine gabbro-schist. Folia- 

 tion also makes its appearance in the main mass, which is here 

 intimately veined with mica-diorite and granite. It is frequently 

 developed near the junction of the gabbro with one of the other 

 rocks. In the small bay known as Pen Voose a lenticular mass of 

 saussurite-hornblende gabbro, measuring about five feet in the 

 longest diameter, occurs in Prof. Bonney's granulitic series. This is 

 evidently not an intrusive tongue, but a lenticular mass which owes 

 its form and position to earth-movements acting after the consolida- 

 tion of the rock. It is conspicuously foliated parallel with the 

 junction surfaces. 



It is instructive to compare the mineralogical with the structural 

 varieties. Foliation is absent from the felspar-diallage rocks. As 

 the foliation becomes more and more pronounced, the diallage is 

 gradually replaced by hornblende, and the felspar undergoes a change 

 resulting for the most part in the development of saussuritic aggre- 

 gates. In the most perfect gabbro-schist the diallage has entirely or 

 almost entirely disappeared, and its place has been taken by horn- 

 blende. It must not, however, be supposed that the mineralogical 

 change is invariably accompanied by the development of foliation. 

 Many of the saussurite-hornblende gabbros are as massive as the 

 original rock. In a paper on the " Metamorphosis of Dolerite into 

 Hornblende-schist " I have pointed out similar relations between 

 structural and mineralogical characters in the case of the Scourie 

 dykes. A molecular rearrangement may take place in a massive 

 rock without the development of foliation ; but there is no reason 

 to believe that foliation of the kind referred to in this communica- 

 tion can take place without molecular rearrangement. 



The principal question which now remains for consideration is the 



