624 DR. G. J. HINDE AND MR. HOWARD POX ON [Nov. 1S95, 



On the high ridge of the northern border of Lifton "Wood, about 

 ^ mile east of Wooladon, radiolarian rocks are exposed in a quarry 

 at its western end. The beds dip 25° S., and a thickness of about 

 20 feet is shown. They are for the most part dark, with light or 

 speckled intermediate beds in which radiolaria can be seen with a 

 lens. There is also another quarry, near the Lodge at the eastern 

 end of the wood, showing a section, about 70 feet in height, of very 

 regular beds of black siliceous rock of a platy or kieselschiefer 

 character which dip 12° S S.E. Microscopic sections of the rock 

 show radiolaria in considerable numbers. Mr. Ussher states that the 

 chert (Codden Hill) beds of this locality are overlain by yellowish- 

 brown conglomeratic beds, but these did not come under our notice. 1 



Beyond Lifton Wood we have not traced the radiolarian rocks 

 any farther in an easterly direction,- but Dr. Holl 2 states that the 

 chert of Gordon Hill extends as far as Sydenham and Leigh Down 

 to Lew Water, which is 4 miles beyond Lifton Wood. 



(g) Tavistock District, Devon. 



At the east end of Tavistock, ascending Greenhill, above the Tavy 

 Iron Works, a road-cutting has been made for a distance of about 

 90 yards through massive beds of a dark, hard, compact, finely- 

 laminated siliceous rock. The dip is not clearly shown, but a 

 thickness of over 30 feet is exposed of the cherty rock which 

 appears to rest on dark clay-shales and to be followed by them. 

 The rock is much traversed by quartz-veins and seems to pass 

 gradually into the clay-shale. In microscopic sections the beds are 

 seen to be crowded with casts of radiolaria now filled with micro- 

 crystalline silica. 



No other exposure of cherty rock was noticed at Tavistock, but 

 pebbles and rounded boulders of dark siliceous rock, occurring in 

 the bed of the river and in trenches lately opened on its bauks, 

 proved, when thin sections were examined, to be filled with 

 radiolaria. 



At Artiscombe, about 2 miles west of Tavistock, just beyond the 

 Lumburn Bridge and near the extensive slate quarry of Mill Hill, 

 there is a quarry mainly of a hard, dark, bluish-grey rock in which 

 there were also some thin beds of a laminated grey, platy, siliceous 

 rock, which proved on subsequent examination to contain numerous 

 radiolaria. As the organic character of the rock was not suspected 

 at the time of our visit, its relation to the other rocks in the quarry 

 was not ascertained. 



Dr. Holl refers 3 to two small outlying patches of Culm Measures 

 at Painter's or Pentre Cross, near St. Mellion, CornwaD, 8 miles 

 W.S.W. of Tavistock, and 4 miles N.E. of Saltash, as the most 

 southerly point at which the Culm Measures had been observed. 

 At one locality, about 600 yards north-west of the Cross, chert 

 occurs, forming the gutter on the east side of the road. It is hard, 



1 Proc. Soni. Archasol. & Nat. Hist. Soc. vol. xxxviii. (1892) pp. 128, 144. 



2 Quart. Journ. Geol. Soc. vol. xxiv. (1868) p. 408. 



3 Ibid. p. 405. 



