468 riiOF. T. G. 1}0>'NEY AND MAJOR-GEN. C. A. ll'^MAHON 



reason of a misunderstanding, but the difference is so remarkable 

 that it seemed worthy of preservation, if only to indicate the 

 caution which must be exercised in selecting a sample for analysis. 



(2) lielation to the older lioclcs. — The serpentine of the Lizard 

 district, as stated by Prof. Bonney, is associated with the sub- 

 divisions of the crystalline schists which were named hj him the 

 Granulitic Group and the Hornblendic Group, but it has not yet 

 been detected among either his Micaceous Group, or the gneisses 

 of very ancient aspect which were discovered by Mr. Fox in the 

 islands fringing the south coast *. 



It wall suffice for the present to say that both the Granulitic and 

 the Hornblendic Group exhibit marked structural characteristics. 

 In the former a dark dioritic rock is sometimes veined, sometimes 

 banded, by one of lighter colour, which often closely resembles a 

 granite ; the latter is very frequently so regularly banded as to 

 suggest an original stratification. Whatever be the significance of 

 these structures — a question which we reserve for the moment — 

 neither rock, in its present state, can be the result of a single 

 operation. 



It has indeed been suggested that all the rocks of the Lizard 

 district are the result of some sort of segregation from one 

 magma f. We do not propose to treat this hypothesis seriously ; but 

 there are three other hypotheses which call for discussion, and these 

 appear to cover the field : that (a) the serpentine (with some of the 

 later rocks) and the older series form an igneous complex which 

 has been afterwards profoundly affected by earth- movements — as if 

 a heterogeneous mass had been passed between a pair of rollers ; 

 {h) the serpentine is really intrusive in the older series, but the 

 relations of the rocks have been so far masked by subsequent earth- 

 movements as to obliterate any conclusive evidence of the intrusion ; 

 (c) the serpentine (as maintained by Prof. Bonney from the 

 first) is intrusive in the older series, and the amount of sub- 

 sequent disturbance has not sufficed in most places materially to 

 disturb their relations. 



Along the eastern coast many sections can be found which exhibit 

 the serpentine and the rocks of the Granulitic Group in intimate 

 association, from Compass Cove to Polbream Point, also about the 

 Frying Pan, and again from the north side of Polbarrow to the 

 Balk. We do not deny that occasional sections may be found in 

 which the present relations of the two are the result of faulting, or 

 which, did they stand alone, might seem to support the view that 

 the granulitic rock was intrusive in the serpentine ; but, after again 

 examining all the sections on both coasts described by Prof. ^Bonney 

 in 1877, we have not the slightest doubt that the serpentine is 

 intrusive in the granulitic rock, which was, at that time, sub- 

 stantially in its present condition, and that, as a rule, their relations 

 have not been disturbed subsequently to any noteworthy extent. 

 The serpentine has broken through the granulitic rock, some- 



* Quart. Journ. Geol. Soc. vol. xliv. (1888) p. 309. 

 t Geol. Mag. (1888) p. 554, (1890) p. 505. 



