18 PROF. T. G. BONNET ON THE [Feb. 1 896 



accuracy of my observations that under ordinary circumstances I 

 should have deemed it needless to revisit the district; but when' 

 two such critics, the one so keen an observer, the other so skilled a 

 petrologist, both entered the lists against me, though in the most 

 friendly contest, I felt compelled to take the first opportunity of 

 revising my work. This was done in the summer of 1 894. Other 

 engagements unfortunately prevented Gen. M c Mahon from giving 

 me the pleasure and the benefit of his company, but I had the great 

 advantage of the society and co-operation of the Eev. E. Hill, with 

 whom I have so often worked in this and other regions, and to whom 

 I tender my best thanks for constant aid. [He has kindly read a 

 proof of this paper, and requests me to say (as I do most gladly) 

 that he can confirm all the statements as to what was seen in the 

 field.] 



Going first to St. Keverne, we succeeded, as we hope, in clearing up 

 a minor difficulty, which our former visit had failed to solve, and 

 we reviewed the hornblende -schists of this neighbourhood. Then, 

 in a fortnight's hard work, from Lizard Town as a centre, we care- 

 fully studied all the sections, as far as Mullion Cove on the west 

 and Kennack Cove on the east, which seemed likely to throw light 

 on the problems specially before us : namely, the genesis of the 

 hornblende-schists and of the so-called < granulitic group,' and % the 

 relations of these rocks to the serpentine and to certain other rocks 

 of igneous origin, but less altered than it. The former problem 

 need not be discussed at any great length, though we accumulated 

 a large number of observations, bearing upon it. The latter one in 

 reality involves the whole question of the relations of the crystalline 

 rocks in the Lizard district, and so demands a rather full treatment. 



II. The Genesis of the Hornblende-schists. 



It will suffice to refer to former papers for descriptions of the 

 petrography of this interesting group. As to the facts, I believe that 

 Messrs. Fox and Teall, Gen. M c Mahon, and myself are practically 

 in accord. 1 Prom the neighbourhood of the lighthouses near Lizard 

 Town to Pollurian Cove on the west (a distance in a straight line 

 of about 5 miles) and to Porthallow Cove 2 on the east (9 J miles), 

 this group, whenever it appears, exhibits substantially the same 

 characteristics. It varies from a dark rock, more or less speckled 

 with white, sometimes so little foliated as to be barely distinguishable 

 from a diorite, occasionally even retaining slight indications of an 

 ophitic or of a porphyritic structure, to one which is clearly foliated 

 and sometimes well banded : dark hornblendic layers alternating 

 with those of a whitish or of a yellow-green colour, the former 

 being rich in felspar, the latter in epidote. The more banded 

 varieties occasionally exhibit a structure which curiously resembles 



1 Quart. Journ. Geol. Soc. vol. xxxix. (1883) p. 1, vol. xliv. (1888) p. 309, 

 vol. xlv. (1889) p. 519, vol. xlvii. (1891) p. 464. 



2 I adopt the spelling of the 6-inch Ordnance map ; formerly it was Porthalla, 

 as in previous papers. 



