Vol. 51.] RADIOLARIAN EOCKS IN THE LOWER CULM MEASURES. 611 



them, so far as their imperfect condition of preservation will allow. 

 We have not, as yet, had an opportunity of studying in the field 

 the relation of these radiolarian rocks to the beds above and below 

 them, except in one or two instances. As the organic character of 

 these rocks has not hitherto been known or suspected, no strict 

 attention has been devoted to the investigation of the character of 

 the rocks which overlie them, and, owing to their disturbed con- 

 dition, the succession is not likely to be definitely ascertained until 

 a regular survey of the area has been carried out. We do not 

 profess to have examined all the outcrops of the radiolarian rocks in 

 the Culm area, and it is very probable that these beds will be found 

 in many localities near the northern and eastern margins of the 

 Dartmoor granite, which we have not had an opportunity of visiting. 1 



In addition to the microscopic organisms, certain limited portions 

 of the radiolarian rocks contain other fossils, some of which were 

 collected by Mr. G. J. Handing, F.G.S., and Mr. G. F. Tregelles of 

 Barnstaple, and obligingly placed at our disposal for examination. 

 In view of the importance of these fossils as showing the geological 

 horizon of the rocks, we have availed ourselves of the kind assistance 

 of Dr. Henry Woodward, F.B.S., P.G.S., to describe the trilobites, 

 and of that of Mr. F. A. Bather and Mr. G. C. Crick to determine the 

 brachiopoda and cephalopoda respectively. 



We also wish here to acknowledge our obligations to Mr. J. J. H. 

 Teall, F.B.S., Sec.G.S., for much valuable advice and assistance; to 

 Mr. J. Hort Player, F.G.S., for making two chemical analyses of 

 the rocks ; and to Mr. W. A. E. Ussher, F.G.S., for readily affording 

 us needful information respecting the best outcrops of the cherty 

 beds. 



II. Literature relating to the Badiolarian (Codden 

 Hill) Beds. 



There is no specific mention of the Codden Hill Beds in the 

 important memoir by the Bev. A. Sedgwick and Boderick I. 

 Murchison on the ' Physical Structure of Devonshire and on the Sub- 

 divisions and Geological Belations of its Older Stratified Deposits,' 2 

 read before this Society in 1837, in which the Culm Measures 

 were first described and delimited from the Devonian, or, as it was 

 then termed, the Grauwacke Series. The authors state that the 

 lower beds of the Culmiferous Series consist of black calcareous 

 shale and black limestone with peculiar fossils, which appear on 

 both sides of the great trough. In describing the shales of the 

 Lower Culm 3 as semi-indurated and as having the separate beds 

 divided into innumerable prismatic masses by small transverse 

 joints, while in the softer varieties the masses are generally rhom- 

 bohedral, and in stating further that they pass into a light-grey, 

 siliceous, jointed flagstone, which in some instances becomes almost 



1 See Postscript, p. 663. 



2 Trans. Geol. Soc. ser. 2, vol. v. pt. iii. (1837) pp. 633-687. 



3 Ibid. p. 671. 



