42 PROF. T. G. BONNEY ON THE [Feb. 1 896, 



opportunities of studying these changes. Towards the outside of a 

 large mass, in a region which has undergone severe pressure, one may- 

 find the ' lenticular ' structure, and it is vain to hope for a decent 

 specimen, but as we pass inward the rock often becomes less 

 brecciated, so that at last fairly normal specimens may be obtained. 

 Even the slaty structure may not affect the whole of a large mass ; 

 now and again portions of it escape comparatively uninjured. Of 

 this, however, we may be sure, that if a force had acted sufficient 

 to produce a marked effect on either the granulite, the hornblende- 

 schist, or the gabbro, the serpentine would have been almost invari- 

 ably torn apart from the weld, and would have been crushed, perhaps 

 to a slate, for at least a considerable distance from the junction. 1 

 If, then, the relations of the serpentine with the granulites and 

 the hornblende-schists indicate an ' igneous complex,' if its structures 

 and those of the gabbro are the results of dynamo-metamorphic 

 action on the rocks when they were solid, the Lizard district 

 flatly contradicts everything which I have learnt about rock-struc- 

 tures during more than twenty years of work in the field and of 

 studying under the microscope specimens collected with my own 

 hands. 



VI. Appendix. 

 (a) Miscellaneous Notes. 



It would be a very long task to examine every rock in such a 

 district as the Lizard, so that even in going over ground compara- 

 tively familiar one picks up ' crumbs ' of information, some of 

 which may be worth a brief record. 



Dykes. — A porphyritic diabase, as described by Messrs. Fox and 

 Teall, and by Gen. M c Mahon and myself, is occasionally found, 

 usually in rather thin dykes. Those hitherto recorded, if not actually 

 confined to the hornblende-schist, are closely associated with it, as 

 near Potstone Point, 2 but we came upon one cutting through ser- 

 pentine (the variety with small crystals of colourless hornblende) 

 near the path 3 leading from Mullion Village to Predannack 

 Wartha. The hornblende-schist, near the western end of the cliffs on 

 the northern side of Porthoustock Cove, is cut obliquely by a yel- 

 lowish rock, generally rather decomposed, which, though only a few 

 inches thick, is more like a dyke than an infiltration-vein. I find 

 this on microscopic examination to exhibit a finely granular struc- 

 ture not resembling any of those usual in veins, and to consist of 

 epidote. This mineral no doubt readily forms as a secondary 

 product in rocks of suitable composition, but the uniformity in 

 .composition is a little strange. Such an epidosite would come most 

 readily from a rock composed of a lime-felspar with some minutely 



1 The effects of pressure are never more conspicuous than in the weaker of 

 •two rocks near the junction-surface. 



2 P. 33. 



3 It is about 350 yards, in a line drawn rather N. of E., from Oreggian 

 Hill ; in the same direction are two other shallow pits in serpentine. 



