J. B. mil— The Pcdceozoics of West Cornwall. 209 



their precise relations with the Devonian formation will now be 

 discussed. While engaged last season on the survey of the tract 

 bordering: the Helford basin, the killas was carried south to Porthallow 

 and westwai-d as far as Tregidden. At Porthallow a fault divides 

 the killas on the north from mica-schist on the south. The rocks 

 lying to the south of that disturbance are not dealt with in this paper. 

 The sedimentary divisions from the Carnmenellis granite, on the 

 north-west, to Porthallow on the south-east, occur in the following 

 topographical order : — 



Mylor Series. 



Falmouth Series. 



Portscatho Series. 



Manaccan Series. 



Veryan Series, including the Quartzite. 

 Of these groups the Manaccan Series represents the Newer 

 Palseozoic,^ and the remainder are confined to the Older Paleozoic. 

 The strike of the latter is about north-east and south-west, while 

 that of the former is slightly oblique and approximates to an east 

 and west direction. 



The Mylor Series, through which the granite has intruded, occupies 

 a band gradually widening in a south-westerly direction from Porth- 

 navas to Gweek. Excellent coast sections across the entire band 

 are aiforded by Polwheveral Creek, showing the whole metamorphic 

 aureole as well as the zone beyond. 



The Falmouth division that succeeds to the south-east forms 

 a narrow band, but widening likewise in a south-west direction. 

 It extends from Mawnan Smith to Mawgan Creek, and is almost 

 entirely confined to the north side of Helford Eiver. Besides the 

 main zone, infolded lenticles occur in the vicinities of Helford, 

 Durgan, and Bream Cove. Excellent transverse sections are 

 exhibited along the coast at Calamansack. 



The Portscatho Series succeeds the Falmouth group to the south- 

 east and forms the coastline as far south as St. Anthony. To the 

 westward it practically monopolises the southern side of Helford 

 Eiver, and the northern shore as far as Porthnavas Creek. It also 

 reappears as a small strip at Porthallow, where it is separated from 

 metamorphic rocks of the Lizard type by a fault. 



The Manaccan Series. — The natural sequence represented by these 

 three Lower Palceozoic groups is now broken, and another assem- 

 blage makes its appearance, which may be designated the Manaccan 

 Series. It rests unconformably on the Portscatho and the Veryan 

 divisions (including the Carne quartzite), and is largely made up 

 of their detritus. The group occupies a band extending westerly 

 from the coast at Nare Point, whence it has been mapped, as 

 far as St. Martin. Passing to the north of Manaccan it is seen 

 along the shores of Gillan Creek, and around the Nare Point to 

 a little beyond the Nare Head. Its southern margin from the coast- 

 line to Treglossack skirts the Veryan Series, and thence to the 



1 The evidence in support of this assumption will be given later. 



DECADE V. — VOL. III. — NO. V. 14 



