200 DR. C. E. TJLLEY ON THE PETROLOGY OF [vol. lxxix, 



a clearer understanding of the chemical and structural changes 

 attending the dynamic metamorphism of hasic igneous rocks. 

 Since that time the investigations of Swiss penologists have shown 

 that Green Schists are widely developed in the Alpine mountain- 

 zones, and have clearly indicated their derivation from lavas, 

 intrusive sills, and associated tuff-heds. In all these eases it is 

 ohvious that the typical epidote-albite-chlorite-schists (prasinites) 

 are the most characteristic low-grade dynamically metamorphosed 

 equivalents of basic igneous rocks. In comparing the Green 

 Schists of the Start area with like rocks of other areas, it will 

 suffice, however, to refer to rocks developed first in the British 

 area, and to a single area from Southern Norway involved in the 

 Caledonian fold-movements. 



(i) The Lizard Area. 



The only area of rocks in the South of England which can hear 

 comparison with the Start district is that of the Lizard. Among 

 the pre-serpentine rocks of this area are developed mica-schists 

 with intercalated tuff-beds, sills, and possibly lava-flows, and the 

 great group of hornblende-schists which enclose the serpentine on 

 the north and south. 



The mica-schists of the Old Lizard Head Series bear comparison 

 with the Start mica-schists, while the hornblende-schists considered 

 by Dr. J. S. Flett as originally lavas and sills are chemically 

 identical with the Green Schists. 



The rocks of the Lizard are, however, in a higher state of 

 metamorphism. The intrusion of the Man-of-War gneisses, and 

 still later the serpentine, has led to the development of contact- 

 minerals in both types of rocks, wherefore mineralogically they 

 differ notably from the Start Group, in which the minerals 

 developed are those characteristic of the upper metamorphic zone 

 of crystalline schists. 



Apart from this divergence in the metamorphic history of the 

 Start and Lizard areas, the sequence of beds and similarity in 

 origin of the rocks of both areas render it not improbable that the 

 two groups of rocks may be of the same age. 



(ii) The ' Green Beds ' of the Scottish Highlands. 



Mineralogically, the Start Green Schists and their accompanying 

 schists of composite origin bear a close comparison with the ' green 

 beds ' of the Highlands. The officers of the Geological Survey 

 have seen fit to regard these rocks as being of sedimentary origin, 

 and produced directly from the erosion of the more basic portions 

 of an igneous complex. 1 



Some of these rocks are microscopically indistinguishable from 

 the schists of composite origin in the Start Group. The mineralo- 

 gical associations of rocks of this type should allow of their use as 



1 See especially Mem. Geol. Surv. Scot. (Sheet 37) 1905, p. 18, 



