28 PKOF. T. Gr. BONNET ON THE [Feb. 1 896, 



blende-schist ? Is it the same as the rock which forms the great 

 cliffs of Carnbarrow and Hot Point, of Housel Bay, and Predannack 

 Head, not to mention other places ? By no means, I should say. 

 True, the dominant minerals are the same in both, and these dykes 

 exhibit locally a trace of foliation. That is also true of other dykes 

 in this region 1 ; nevertheless, the hornblende-schist proper, as a rule, 

 is a very different rock, even macroscopically. It is commonly more 

 or less banded, almost always distinctly * linear ' in structure ; only 

 rarely and only very locally would there be any difficulty in dis- 

 tinguishing the one from the other. I find that the same holds good 

 of the microscopic structure of the two rocks ; the differences can 

 hardly be expressed in words, but as a rule they exist. What, then, 

 does this prove ? That sometimes, if we take two hand-specimens, 

 carefully selected from two groups of rocks, differing in age and 

 history, we may be unable to distinguish the one from the other, 

 because neither presents characters upon which we can fasten for 

 that purpose. We might as well affirm that the Greek and the Latin 

 uncial alphabets belong to the same language because certain letters in 

 the two are identical. Has any one of these dark pyroxenic dykes 

 in the Lizard region exhibited such a banded structure as that which 

 occurs again and again in the ' hornblendic ' group ? It would be, 

 in my opinion, just as reasonable to contend that the hornblende- 

 schist was only a modification of the gabbro, 2 because now and 

 again, though very locally, resemblances can be detected ; or that 

 all the basalt dykes of Scotland were of one age, because it is not 

 always easy to say whether a particular one belongs to the Palaeozoic 

 or to the Tertiary era. (b) ' The dykes near the Lion Rock, in 

 their thicker parts, sometimes resemble the granulitic group.' To 

 this we may reply in terms similar to those already used. Once or 

 twice a dyke may be found to exhibit some rather irregular f el- 

 spathic veins or seams. But this, so far as my experience goes, is 

 not a very uncommon feature in districts such as the Lizard. The 

 resemblance between the two rock-masses seems to me hardly closer 

 than the notorious one between Monmouth and Hacedon. I have 

 found it difficult in other places to distinguish between veins of 

 infiltration and of intrusion, yet this does not prevent me from 

 believing that each really exists, and can be often identified. So 

 that in this case also, while I grant that certain resemblances may 

 be found, I deny that they are sufficient to warrant the conclusions 

 which have been drawn from them. 



(«) Relations of the Serpentine to the Granulitic Rock. 



But I pass from generalities to particulars, and first to 'the 

 wedge-shaped mass of typical granulitic rock.' There can be no 

 question that this — like the great masses which crop up on the 



1 Quart. Journ. Geol. Soc. vol. xxxix. (1883) p. 6 (reference). 



2 If so, there should be no ' complex,' for the gabbro cuts the serpentine 

 again and again. 



