622 DE. G. J. HINDE AND ME. HOWAED FOX ON [Nov. 1 89 5, 



Prof. Phillips l refers to the beds at this place as soft and hard, 

 white, pink-stained, and black, the equivalents of the Codden Hill 

 grits, with quartz-veins ; below these are laminated grey grits and 

 shales, then thick dark grey or black limestone covered by black shale 

 resting on trap. 



Following the high road eastwards along the summit of the 

 ridge, near St. Stephen, about 2 miles from Launceston, are two 

 quarries, one on each side of the road, in which similar hard black 

 and grey cherty rocks with radiolaria are shown. The beds dip 

 W. at 21°. 



On the same ridge, north of St. Stephen, in the Castlehill 

 plantation, about 1^ mile from Launceston, is a quarry which on 

 the 6-inch Ordnance Survey map is marked as Barracadoes Quarry 

 (killas). The beds in it, however, are not at all of the nature of 

 killas, but consist mostly of light-tinted, banded, very hard, siliceous 

 rock with interbedded soft, grey, shaly beds, which are crowded 

 with radiolaria and sponge-spicules. The face of the quarry is 20 

 to 25 feet in height ; the beds dip 28° north. 



Another exposure of nearly similar chert and shale is shown by 

 the roadside near Dutson, about 1 mile S.S.E. of the Barracadoes 

 Quarry. The beds dip N. 10° W. at 38°. Lenticular patches of 

 volcanic materials are interbedded in the cherty rocks at this place. 

 Some of the beds here have a porous structure, the cavities appa- 

 rently arising from the dissolving-out of small crystals. Traces of 

 radiolaria can be occasionally seen in the rock, but only after 

 careful search. 



According to Dr. Holl, 2 the beds of chert (or radiolarian rock) on 

 St. Stephen's Down and west of it, towards Tregeare Down, occupy 

 the centre of a synclinal trough, the underlying Devonian rocks 

 being brought up to the surface along a narrow axis on the north, 

 which extends from Underwood Parm to Yeolm Bridge, while a 

 lower axis on the south ranges east and west through the town of 

 Launceston. 



In a small quarry near Landlake Cross, about a mile east of 

 South Petherwin and 2^ miles south of St. Stephen's Badge, 

 there are beds of hard black and grey, platy, siliceous rock, dipping 

 E.S.E. at 25°, which contain radiolaria, sometimes in great abund- 

 ance, and also sponge-spicules, and resemble in other respects the 

 cherty rocks of St. Stephen's Down. As mentioned by Mr. Ussher, 3 

 these beds are situated within the general boundary of the Devo- 

 nian, and have been included with this formation in De la Beche's 

 map. 



Parther eastwards we next meet with radiolarian rocks at Gordon 

 Hill, a ridge 440 feet in height, about two miles E.S.E. of Laun- 

 ceston, and thus on a parallel more to the south than the beds of 

 St. Stephen's Bidge. On the southern slope of the hill, at the 

 village of Carzantic, is a quarry showing the best exposure of these 



1 ' Pal. Fobs. Cornwall, etc.,' 1841, p. 195. 



2 Quart. Journ. Geol. Soc. vol. xxiv. (1868) p. 410. 



3 Proc. Som. Areha:ol. & Nat. Hist. Soc. vol. xxxviii. (1892) p. 132. 



