Yol. 51.] RADIOLARIAN EOCKS IN THE LOWER CULM MEASURES. 623 



rocks in the Launceston district (PI. XXIV.). There is a regular 

 succession of beds, mostly of grey and bluish-grey rocks, but with 

 some of a dark tint as well, consisting of hard, brittle, compact 

 chert without admixture of soft shaly beds. A thickness of about 

 50 feet is shown, and throughout the series radiolaria can be distin- 

 guished, being in some beds thickly crowded together. The face of 

 this quarry is from 40 to 50 feet in height ; the beds dip N.W. at 

 18°. Dr. Holl states ' that the chert of the high ground of 

 Gordon Hill is underlain on the north by black slate and the 

 limestone south of Timber Bridge. 



At Wooladon, on the north-eastern side of the River Tamar, about 

 a mile distant from the Carzantic quarry in a direct line, and close 

 to the Great Western Railway and the river, an extensive section 

 of the Lower Culm Measures is shown in the face of the quarries 

 formerly worked for limestone, which are marked in the 6-inch 

 Ordnance Survey map as Lifton Quarry. The lowest beds exposed 

 are the dark limestones and shales ; these are succeeded above by 

 thinly laminated, pyritous black shales containing impressions of 

 Posidonomya, followed by a considerable thickness of grey, buff, 

 and white shales, in places separating into thin papery laminae and 

 minutely porous, which resemble in general appearance the soft 

 radiolarian shales associated with the harder beds which occur in 

 the other quarries of this district, but at this place no organisms can 

 be seen in them. In the lower limestones, however, there are 

 traces of sponge-spicules as well as some rounded bodies resembling 

 radiolaria, but now infilled with calcite. 



Above the papery shales, and forming the top beds of the quarry, 

 there are thick and uneven beds of bluish cherty rock traversed by 

 numerous veins of quartz. These are best shown on the southern 

 side of the ' old quarry,' now filled with water, where they dip to 

 the south. Radiolaria are present in this rock, which appears to be 

 the lower portion>of the Radiolarian Series, and if, as seems to be 

 the case, the beds are here in their regular succession, they demon- 

 strate a definite upward sequence from the dark limestones and 

 shales with Posidonomya through beds of soft shales to the cherty 

 rock with radiolaria. Mr. Ussher 2 refers to this Wooladon section, 

 and mentions that in its upper portion phthanites or Codden Hill 

 Reds are present. 



At Lifton Down, about \ mile due north of the western end of 

 the Wooladon quarry and at a higher level, somewhat similar beds 

 of hard dark and bluish cherty rock, traversed by quartz-veins and 

 accompanied by light siliceous shales, are exposed. The beds are 

 much compressed, and in the chert only a few indications of radio- 

 laria could be seen; but the shaly beds, which have become hard and 

 platy and interpenetrated with numerous minute strings of quartz 

 in the same way as the chert, show in thin sections radiolarian 

 casts in abundance. 



1 Quart. Journ. Geol. Sop. vol. xxiv. (1868) p. 408. 



2 Proc. Som. Archseol. k Nat. Hist. Soc. vol. xxxvi. (1890) p. 100; also 

 vol. xxxviii. (1892) p. 127. 



