560 Green &f Sherboni — Pollurian Coast, Cornwall. 



Porthscatho Beds in the first 50 yards of the shore section. 

 Traces of the Falmouth. Beds can be found here and there on the 

 fields to the west of the Helston-Lizard road, but the bulk of 

 tlie debris is of Porthscatho age, and we consider that nearly the 

 whole oE the Falmouth Beds have disappeared except for the 

 small patches described as existing on the coast, and the similar 

 patches preserved by infolding among the Porthscatho on the land 

 surface. 



The peculiar characteristic rock of the Lower Portliscatho — the 

 massive detrital rock like the well-known Grampound Grit — is seen 

 but once north of Looe Bar (just past the Looe outfall), but this bed 

 may be an ash-bed in the Upper Porthscatho of similar nature to the 

 characteristic rock. 



We consider all the ' Mylor ' Beds of the Survey as the upper part 

 of the Porthscatho, which in our opinion continues right up to the 

 granite at Trewithick. 



Thei'e is a very interesting little infold of slate Avith inclusions at 

 the Looe Bar outfall, associated with the ' ash-bed ' mentioned above. 

 This is similar in appearance to some of the Veryan, but the great 

 mass of the Lower Porthscatho which comes over the Ver5'an does 

 not occur at this point, and one must regard the bed as of merely 

 local stratigraphical interest belonging to the Upper Porthscatho 

 Series. 



The Upper Porthscatho consists of thick gritty slates, which 

 weather yellow, bands of gritty slates weathering ashy-grej^, and 

 black micaceous sandy slates locally called ' blue-stone '. Quarries 

 are not abundant, and the first sign of ' spotting ' in the slates 

 we met with was north of Tremearne Cliff at the 212 feet level 

 on the main road about a third of a mile from the granite of 

 Trewithick. 



Having examined this fine coast-section we see no leason to alter 

 the opinion expressed by one of us (Green, Geol. Mag., 1904, 

 p. 401 ; 95th Ann. Bep. Roy. Cornwall Geol. Soc, 1908, p. 7) 

 that the whole of these beds — Dartmouth, Falmouth, Ladock, 

 Grampound, Manaccan, Mylor, Porthscatho, and Veryan — whatever 

 they may be designated, are of Gedinnian age and liave nothing to do 

 with Silurian, Ordovician, or Cambrian rocks, and we consider the 

 stratification of the older Cornish rocks from above downwards to be 

 as follows : — 



^Falmouth (includes beds called Dartmouth). 



^ _ Porthscatho (mcludes beds called Mylor, Grampound, 



T ^„.„„ T^ „,Z.^.i Ladock, and Manaccan). 



Lower Devonian U^ ,,' , ,..',,., ■ ^ ■ ■ ^^■ 



Veryan (beds contammg lenticular mclusions yieklmg 



\ Ludlow, Wenlock, and Woolhope fossils). 

 Ordovician. Quartzites^ (of Ordovician age with characteristic fossils). 



^ That the Ordovician Quartzites of the Gorran-Veryan-Manaccan anticline 

 once existed in this area is evident from the abundance of the rock in the walls 

 at White Cross and elsewhere. As it is continually being broken up for road- 

 metal, the dotted lines on the old one inch map (Sheet 13, 1839 and 1866) of 

 De la Beche will soon be the main record of its existence in the area. 



