664 DR. G. J. HINDE AND ME. HOWARD FOX ON [Nov. 1 895, 



some bands crowded with radiolaria, with intermediate bands of 

 siliceous shale. The limestone in this quarry is seen in thin section 

 to be largely crystalline, with a few traces of organisms. 



At Sourton Down, about a mile N.E. of the quarry just men- 

 tioned, there are two small quarries of chert on the crest of the 

 hill, and the summit of the hill appears mainly to consist of chert. 

 The beds are much folded and contorted ; a thickness of 10-12 feet 

 is shown. The chert is laminated, bluish, weathering grey, and tra- 

 versed in all directions by fine quartz-veins. Radiolarian casts may 

 be distinguished in it both with a lens and under the microscope. 



On the south side of the Higher Collaven railway-bridge, about 

 half a mile east of the Sourton quarry, there are layers of dark 

 chert interbanded with dark and blue flinty rock, probably shale 

 altered by contact with igneous rock (greenstone?) which here 

 comes in. Microscopic sections of the chert show numerous radio- 

 larian casts, which are infilled with cryptocrystalline silica. 



Okehampton. — In the railway-cutting on the eastern side of the 

 Meldon 1 viaduct of the L. & S.W. Railway, between two and three 

 miles from Okehampton, a section, about 25 feet in height, of 

 beds dipping N.N.W. is exposed. The rock is principally a black, 

 compact chert, associated with dark, indurated shales. The chert 

 contains radiolaria. 



In the railway-cutting about one mile west of the Meldon 

 viaduct, banded dark- and light-bluish flinty rocks, resembling 

 porcellanized shale, are exposed near the band of igneous rock, 

 in the same manner as at the Higher Collaven bridge. Mr. TJssher 2 

 has noticed these beds as belonging to the Basement Culm series. 

 It may be mentioned that the dark chert is used for ballast on the 

 railway in this district, and the radiolaria in it can be readily 

 distinguished with a lens. 



At the quarry by the public road at the south-western end of 

 Okehampton, beds of limestone alternating with shales are shown, 

 which dip N.N/VV. at an angle of 55°. About 300 yards north of 

 this quarry, on the western side of Church Hill, there are thick beds 

 of black chert and shale ; the chert has numerous quartz-veins ; no 

 radiolaria can be seen in it. 



About 4 miles east of Okehampton are the extensive Lower 

 Culm Limestone quarries of South Tawton. In the lower part of 

 the quarry at present worked, about 60 feet of dark limestone 

 with shales are exposed. The succession is best seen at the disused 

 quarry, now full of water, nearest the village, where the limestone 

 is seen to be cverlain by dark carbonaceous shales, succeeded by 

 pale-grey and buff soft shales, and at the summit by beds of chert 

 and shale which form conspicuous prominences. The chert is 

 compact, bluish, and thickly traversed by veins of quartz ; in a 

 microscopic section numerous casts of radiolaria are shown. 



Drewsteignton.- — At the large limestone-quarries close to this 

 village, a section of about 80 feet in thickness is at present exposed. 



1 'Elmdon' on the 1-inch Geol. Surv. map. 



2 Proc. Som. Archaeol. & Nat. Hist, Soc. toI. xxxviii. (1892) p. 136. 



