620 DR. G. J. HINDE AND HE. HOWARD FOX ON [Nov. 1 895, 



limestones, and sections of these show faint outlines of radiolaria 

 and sponge-spicules. Some of the limestones are foraminiferal and 

 contain a small form of Endoihyra. 



We have thus traced the radiolarian rocks along and within the 

 northern boundary of the Culm Measures and the Upper Devonian 

 from Templeton, west of the Taw River, near Barnstaple, to Ash- 

 brittle in West Somerset, a distance of about 31 miles in a direct 

 line. 



(e) Boscastle District, Cornwall. 



We now proceed to follow the outcrop of the radiolarian rocks on 

 the southern margin of the Culm Measures, within, that is, north 

 of the boundary-line between them and the Devonian, which is 

 marked on the Geological Survey map as running from near Boscastle 

 on the coast in a generally E.S.E. direction to the west side of the 

 granite of Dartmoor near Tavistock. 



As De la Beche pointed out, 1 the lowest beds of shale and arena- 

 ceous rocks belonging to the Culm series make their appearance 

 in a bay between the Meachard Bock and Short Island, immediately 

 south of Boscastle Harbour. For a distance of a little more than 

 1| mile from this place, in a N.E. direction, the coast-cliffs ex- 

 hibit a succession of highly folded and contorted slates and grits, 

 having a general dip to the north of about 25°, up to the northern 

 end of what is marked on the 1-inch Ordnance Survey map as Beeny 

 Cliff. At Fire Beacon Point, on the summit of the cliff, 469 feet 

 above sea-level, there is a conspicuous ridge of cherty rock which 

 extends northwards for a distance of 600 feet, and is shown on the 

 slope of the cliff to within 150 feet of the beach. The chert rests 

 on dark fine-grained slates or shales, which can be followed down 

 for a distance of about 150 feet before there is any appearance of 

 grits. The cherty rock itself, making due allowance for the folding 

 of the beds, must be over 80 feet in thickness. It is mainly a very 

 hard, dark or black rock, showing in places lines of lamination ; 

 it has been intensely squeezed and contorted, and it is traversed 

 throughout with veins of white quartz. Near the base this rock is 

 interbanded with and gradually passes into hard, dark, fine shales. 

 Under the microscope the dark cherty rock is seen to consist of 

 cryptocrystalline to microcrystalline silica with a considerable 

 amount of dark material, either disposed in laminae with light 

 interspaces or dispersed generally throughout the rock. In the 

 darker portions there are only a few indistinct casts of radiolaria, 

 but in the lighter specimens they are more numerous, though but 

 faintly shown. On the whole this Beeny Cliff rock might be termed 

 an impure chert, in which the organic structures are nearly obli- 

 terated by the admixture of the dark carbonaceous material and the 

 intense pressure. 



Above the chert dark shales again come in, and as far as Fox 

 Hole Point, north of Millook, about 5 miles distant from Beeny 



1 'Report Geol. Cornwall, etc.,' 1839, p. 106, pi. iv. fig. 1. 



