pait 2] THE METAMORPHOSED ROCKS OF THE START AREA. 193. 



At Southpool Creek the junction-beds ai'e Green Schists, and 1 

 the development of an ironstone band marks the fault-plane. The 

 fault-zone at Hope is characterized by an abundant development 

 of quartz-veins and segregations. 



The marked distinction in petrographic character of the rocks 

 on either side of the boundary, the persistent development of 

 alteration in the rocks along the boundary, and the structural 

 discontinuity in the Southpool- Creek section, lead inevitably to. 

 the conclusion that the boundary-line represents a plane of major 

 dislocation, bringing together rocks of different origin and 

 markedly different grades of metamorphism. 



Taking into consideration the known direction of movement of' 

 the Armorican folding which has affected the Devonian and 

 Carboniferous rocks of the South of England, we might expect 

 that the boundary of dislocation should show some evidence of a 

 northward overthrust movement corresponding to the northward 

 stresses of this post-Carboniferous movement. The evidence of' 

 the boundary, so far as it can be interpreted, does not, however,, 

 support this view. 



The direction of cleavage-dip of the Devonian slates immediately 

 north of the boundary-line is uniformly northward, and there is no ■ 

 evidence to suggest that the major fault-plane hades in a southerly 

 direction. 



VII. Nature of the Metamorphism. 



The interpretation of the boundary of the Start Schists with 

 the Devonian rocks lying on the north, as a plane of major dis- 

 location, raises questions of interest in regard to the age of these 

 rocks and their metamorphism. It must be admitted at the 

 outset that these questions, through lack of definite evidence, are 

 not at present capable of complete solution. The same problem, 

 in fact, as that which has confronted investigators of the Lizard 

 area confronts the investigator here. No one has yet discovered 

 any evidence of organic remains among the sedimentary mica- 

 schists of the Start area. 



Petrographically, the rocks are allied in some ways to the pre- 

 serpentine rocks of the Lizard : namely, the mica-schists and . 

 hornblende-schists into which the plutonic complex of the Lizard 

 is intruded. Mineralogically, the Green Schists bear considerable 

 resemblance to the 'green beds' of the pre-Cambrian of Scotland. 

 It is clear however that this group of rocks was involved in a 

 pre-Devonian epoch of folding, and one during which the essential 

 metamorphic features of these rocks were impressed upon them. 

 In Britain, among Palaeozoic rocks, no assemblage is known having 

 their petrographic character. In Western Norway, however, rocks 

 of this tj'pe (phyllites, mica-schists, and green schists of Cambrian 

 to Silurian age — particularly Lower and Upper Ordovician) are 

 found, as in the Stavanger district and elsewhere. These rocks 

 have been subject to metamorphism during the Caledonian epoch. 



