Vol. 52.] ROCKS OF THE LIZARD DISTRICT. 49 



EXPLANATION OF PLATE I. 



Pi". 1. Intrusive serpentine, streaked brownish and blackish, from near Pare 

 Bean Cove (see fig. 10 and description in text, p. 35). a is a band 

 of the orange-coloured serpentinous mineral ; the other bands (b) are 

 lighter in colour, but often speckled with a light puce-brown and with 

 opacite. The large dark grain is of a deep brown tint. (X 8.) 



2. Prom a band of serpentine, intrusive in hornblende-schist, and including 



a thin ' streak ' of the same, from the section described near Pare Bean 

 Cove (see description, p. 36). The part drawn represents the junc- 

 tion of the serpentine with the included streak of schist, a, film of 

 true serpentine, forming outer part of specimen ; b, fibrous minerals 

 — brownish hornblende, chlorite (?), etc. ; c, more granular brown horn- 

 blende, and dark ' earthy ' spots (decomposed felspar). ( X 8.) 



3, 4. Junction of serpentine and hornblende-schist near 'Potstone Point/ 



The two rocks, as described in the text, are ' fused ' together. In order 

 to represent this better, 4 is in part a repetition of 3, the lower por- 

 tion of the former corresponding with the upper portion of the latter. 

 a represents the serpentine with a fluxional structure. It contains 

 grains of brown hornblende, which are more conspicuous near the 

 junction b ; c is hornblende-schist (with brown hornblende), between 

 which is a greenish mineral, often serpentinous in aspect, as described 

 in the text (p. 33). (X 12.) 



5. Serpentine interstreaked with hornblende-schist, which it has partly- 



fused, from Potstone Point (see p. 33). a, mostly a rather fawn- 

 or orange-coloured serpentine, including brownish hornblende, etc. ; 

 b, hornblende-schist with brown hornblende and earthy material 

 (the part dark in the drawing) representing the felspar. ( X 9.) 



6. Another specimen from the same locality, showing a more complete 



interstreaking of serpentinous (a) and hornblendic (b) layers, as if the 

 two rocks had flowed together like a slag. ( X 9.) 



Discussion. 



Mr. Teall said that, although he had visited the Lizard several 

 times, he had been unable to form any general theory as to the 

 structure of the district. He was glad to find that, so far as the 

 facts were concerned, there was no serious difference of opinion. 

 The question of the relation of the granulitic series to the serpentine 

 was complicated by the occurrence of veins and dykes of both acid 

 and basic rocks cutting serpentine and gabbro. He could not, in 

 all cases, separate these from the corresponding rocks of the granu- 

 litic series. He called attention to photographs and clay models 

 illustrating his theory that the granulitic rocks were of igneous 

 origin, and that many of the peculiar structures were the result 

 of deformation. The Author had accepted the igneous origin of the 

 granulitic rocks, and considered that the deformation took place 

 when the acid rock was intruded. 



The main object of the joint paper by himself and Mr. Pox, so 

 far as it related to the section near Ogo-dour, was to call attention 

 to the interbanding of the serpentine and schist, and to the folding 

 which had affected the banded series. He thought that infolds had 

 sometimes been mistaken for intrusive tongues, and he pointed out 

 that transgressive junctions might be produced in connexion with 

 folding. He preferred the interpretation which he and Mr. Eox 

 had arrived at to that proposed by the Author. 



Q. J. G. S. No. 205. e 



