ON THE CRYSTALLINB HOCKS oF Till; LIZARD DISTKICT. 



471 



Bome peculiarities *, which we consider to bo the result of contact- 

 motamorphism. Again, in a liltle pit on Carnbarrow, at the top of the 

 cliffs, a " slabby " piece of banded hornblende-schist, about 8 inches 

 thick, is completely surrounded by serpentine. Lastly, there are 

 the junctions at Porthalla, which must he described in rather more 

 detail, as Prof, lionney's interpretation has been questioned in 

 the pages of this Journal by Mr. J. H. Collins t, who maintains 

 that there is a gradual transition from the hornblende-schist to the 

 serpentine, the latter being regularly interbanded or interstratified 

 with the former. We find, instead of the orderly arrangement 

 depicted in his published section t, that a mass of serpentine breaks 

 through the hornblende-schist, and runs diagonally, roughl}^ in a 

 westerly direction, up the craggy face of the hill §. Above it is a 

 great mass of hornblende-schist, generally with little banding or 

 foliation, and thus dioritic in character. At a short distance below 

 it are exposed the rather fissile schists referred by Prof. Bonney 

 to the Micaceous Group, the intervening space being concealed by 

 debris. But in three or four places on the rocky shore, between 

 tide-marks, or just above high water, the relations of the serpentine 

 and schist are well displayed. For instance, rather on the western 

 side of the serpentine, slabs of banded hornblende-schist occur in 

 that rock, the lower about three feet thick, the upper about one 

 foot ; the intervening space, rather more than two feet thick, 

 being occupied by serpentine || (fig. 3). 



Fig. 3. — Section at the foot of the cliffs, Porthalla. 



1. Serpentine. 



2. Hornblende-schist, about 3 ft. 



3. Serpentine, about 2^ ft. 



4. Hornblende-schist, about 1^ ft. 



5. Serpentine. 



* See below, p. 473. 



t Quart. Journ. Geol. Soc. vol. xl. (1884) p. 458; Geol. Mag. (1885) p. 298, 

 and (1886) p. 359. 



J Quart. Journ. Geol. Soc. vol. xl. (1884) p. 401, fig. 2. 



§ Since the publication of Mr. Collins's paper, I have been thrice at Porthalla. 

 On one occasion I had with me a copy of Mr. Collins's published section, and 

 we sought to reconcile it with what we saw. After using our best endeavours, 

 we were obliged to abandon the task as hopeless. Gen. M^^Mahon had also 

 visited Porthalla in 1887, and had met with no better success. The junction 

 of the serpentine and hornblende-schist, which I saw in a quarrj' in 1882, had 

 disappeared by 1880, and cannot now be found.— T. G. B. 



II Obierved and drawn in 188G.— T. G. B. 



