Yol. 52.] 



ROCKS OF THE LIZARD DISTRICT. 



29 



I have probably examined in the field more of these rocks — espe- 

 cially the latter — than most geologists, yet I have never seen a 

 branching vein, and only two or three dykes. 1 The mode in which 

 this rock occurs generally suggests that it was extruded in a rather 

 * pasty ' condition ; sometimes also that the temperature was not 

 very high. 2 



But though the serpentine does not send veins into the * granu- 

 lite,' its relations to that rock appear to me generally to suggest 

 and sometimes to prove intrusion. Take, for example, this instance 

 from Polbarrow Cove (fig. 4), where a fragment of serpentine about 

 14 inches long, 3 to 5 inches 



wide, and seemingly about Fig. 4.— Serpentine adhering to a 

 3 inches thick, still adheres « step > f granulite, in Polbarrow 



to the granulite, which is Cove. 



particularly evenly-bedded 

 (reddish grey with dark- 

 coloured) for about half a 

 yard above and a yard 

 below. Some two or three 

 yards behind the top of 

 the craglet is another and 

 longer mass of serpentine 

 which appears to occur in 

 a similar fashion. Or this 

 case from the same cove (fig. 5), where the junction-surface is ir- 

 regular, the granulite for a short distance is disturbed, and two or 

 three small fragments 



of it occur in the ser- Pig. 5. — Banded granulite {with fragments 

 pentine. Or this one in serpentine), south of Poltesco Cove. 



from Enys Head, 



where the serpentine 

 seems to have forced 

 open the granulite 

 along the lines of 

 banding, rumpling 

 those in its imme- 

 diate neighbourhood 

 (fig. 6, p. 30). Or this 

 other one from the 

 same locality, where ^%2s> 



the junction-surface is 



puckered and squeezed up, while in one case (as shown in fig. 7, 

 p. 30) the bands of the granulite are cut off by the serpentine. 

 We found another, and a very marked instance of the same kind, 





1 I do not forget the case in Forfarshire described by Sir Charles Lyell, but 

 I have not been in that part of Scotland. 



2 I may add that in districts where the rocks have undergone much mechani- 

 cal disturbance, the junctions, as a rule, are spoiled. Serpentine is a brittle 

 rock, and commonly yields to strains before its neighbours, so that a line of 

 junction is generally a line of fracture, and often of complete ' smash.' This 

 rule is almost universal in the Alps. 



