ON THE CRYSTALLINE ROCKS OF THE LIZARD DISTRICT. 405 



explain, in certain cases, the banded arrangement of the constituent 

 minerals *. 



In the summer of 1S90 the authors of the present paper met 

 at the Lizard in order to discuss the whole question on the 

 spot. They hoped bj' this means to bear united testimony as to 

 the facts of nature and to avoid many opportunities for misunder- 

 standing, while any diversity of opinion as to the interpretation 

 of the former could be easily expressed. They were joined by the 

 Rev. Edwin Hill, to whom they are indebted for constant help in 

 iield-work and in discussion, both by suggestions and by criticism. 

 They believe that they may add his name as a witness to the 

 facts recorded in this paper, and do not expect to find any serious 

 difference of opinion on his part as to the main questions of inter- 

 pretation. 



During a fortnight's stay at the Lizard, followed by about four 

 days at St. Keverne, they examined de novo almost all the more 

 important coast-sections of the Lizard peninsula as far north as 

 Mullion Cove on the west and the Nare Head on the east t. They 

 had also the great advantage of going over some of the most critical 

 sections with Mr. Teall, to whose views reference has already been 

 made, and with Mr. Fox, to whose acute observation and conscien- 

 tious work in this district geologists are so greatly indebted. The 

 hours spent in frank interchange of opinion and in friendly discus- 

 sion of views, sometimes divergent, were no less pleasant than 

 profitable, for, in more than one instance, they removed miscon- 

 ceptions and demonstrated that the shield, if gold on one side, was 

 silver on the other. 



II. The Serpentine. 



In regard to the serpentine, the majority of competent observers 

 are in general agreement. Hence it may be convenient to consider 

 this rock first in order and use it as a kind of datum-line for the 

 other rocks of the district, which will then be found to fall into 

 two rather distinct classes. In dealing with the serpentine three 

 subjects call for special attention : — (1) its origin and composition ; 

 (2) its relation to the rocks of earlier date ; (3) the significance of 

 its structures, if any. 



(1) Origin and Com^po^ition. — These subjects have been so fully 

 discussed by Prof. Bonney in his two papers and by Mr. Teall in 

 his " British Petrography " that little more need be said. But, 

 for convenience of reference, we have exhibited in tabular form the 

 constituent minerals (other than serpentine) of the rocks noticed 

 by these authors, to which have been added one or two varieties 

 hitherto undescribed. The derivation of serpentines which exhibit 



* Quart. Journ. Geol. Soc. vol. xlv. (1889) p. 519. 



t Want of time prevented tlieui from examining the cliffs for about a mile 

 on either side of the Blackhead. These are rather difficult of access, and 

 •consist, according to the. Survey map, of serpentine, so that they did not seem 

 likely to throw additional light on any question except those on which the 

 authors were already satisfied. 



