40 PROP. T. G. BONNET ON" THE [Feb. 1 896,. 



tification, but here and there in it are zones of larger flakes, in part 

 at least actinolitic, spotted with grains of haematite and of a 

 pyroxene, in some cases certainly hornblende. 



Whether the whole of these two masses, which I formerly 

 supposed to be mainly altered and decomposing hornblende-schists y 

 consists of serpentine streaked with bands, which are more nearly 

 picrites in composition, it would be impossible to say without 

 another and yet more minute examination, and this, perhaps, after 

 all would hardly repay one for the trouble ; for it is now clear that 

 this section affords a conspicuous instance of a banding in the- 

 serpentine itself. As to the two larger, apparently included, masses 

 of ' brownish-grey ' rock, I incline to regard them as pieces of a 

 picrite, rather than as exceptionally altered fragments of the horn- 

 blende-schist, but in the present state of my knowledge cannot 

 venture to speak more positively. 



Y. Conclusions. 



I submit, then, that the facts described in this paper justify the 

 following conclusions : — 



(a) Mechanical forces, due to earth-movements, have only rather 

 locally produced important effects on the crystalline rocks of the 

 Lizard : namely, in a very limited area at Porthallow, near the 

 great boundary-fault, and over a larger one in the south, approxi- 

 mately bounded by a line drawn from a little east of Polpeor to 

 rather south of Caerthillian Cove. 1 



(6) Elsewhere the results of such forces are of very secondary 

 importance, being restricted to the neighbourhood of faults, and 

 even there producing commonly very limited effects. 



(c) The slightly foliated or linear structure rather common in the 

 serpentine, its occasional distinct banding, together with rather 

 similar structures in the gabbro and a faint approach to them in 

 certain basic dykes, as has been more fully shown in the paper by 

 General M c Mahon and myself, have nothing to do with ' dynamo- 

 metamorphism,' but have been produced by fluxion-movements 

 anterior to the complete consolidation of the rock. 



(cQ The serpentine is intrusive in the ' granulitic group,' which, 

 however (though it may have torn off large blocks), it has- 

 only locally softened and indented. It is also intrusive in the 

 hornblende-schist, but this it has sometimes riven, and occasionally 

 melted down, in certain cases partially, in others perhaps whoUy,. 

 thus producing the streaks of a less pure character, with some 

 resemblance to the former rock : these phenomena, as might be 

 expected, being restricted to the exterior of the mass, the rest of it 

 generally exhibiting an uniform character for considerable distances. 



In short, though the effect of twelve years' work in the field and 

 with the microscope has caused me to change my views as to the 



1 An area very nearly correspondent with that assigned to the ' mica-slate 

 series' of Sir H. De la Beche. The line, if it runs straight (I have not attempted 

 to trace it), would be roughly from N.W. to S.E. 



