214 DR. G. J. HINDE ON RADIOL AEIA. IN CHERT [May 1899^ 



12. On Eadiolaria in Chert //-om Chtpons Farm, Mullion Parish 

 (Cornwall). By George Jennings Hinde, Ph.D., F.R.S.,. 

 P.G.S. (Read February 1st, 1899.) 



[Plate XVI.] 



I. Introductory Remarks. 



At the time of the discovery of the Radiolarian Chert-beds on Mulliori' 

 Island in 1893, described by Messrs. Fox & Teall,^ the extension of 

 the beds to the neighbouring mainland was suspected, but no traces 

 of them conld be found. Mr. Howard Fox, however, continued his 

 search for them, and in the early part of 1897 he discovered a small 

 exposure of chert in situ, in a road-cutting near the base of the 

 hill leading north from Chypons and about 1 mile north by east 

 of Mnllion Church. The chert appears as several bands interbedded 

 with the clay-slates of the district. Detached blocks of chert had 

 previously been noticed on the surface of the fields and built inta 

 the hedges in the neighbourhood, but up to Mr. Fox's discovery the 

 rock had not been recognized or recorded in place. Mr. Fox caused 

 microscopic sections to be prepared from different portions of the 

 chert-bands, and these showed the presence of radiolaria in 

 considerable numbers, resembling in general appearance the forms 

 present in the chert from Mullion Island. In some portions of the 

 chert, however, the radiolaria were preserved in an unusually 

 perfect condition, showing their latticed structure and spines very 

 distinctly, and Mr. Fox forwarded to me the specimens, and some 

 careful drawings by Miss Lister of the organisms, in order to see 

 whether any fresh knowledge respecting the character of the radio- 

 laria could be obtained. As some of the forms appear to be new, 

 and as they are more favourably preserved thati any previously 

 described from the Palaeozoic rocks of this country, I have ventured 

 to bring them before the Society. 



The Chypons cherts which yield the radiolaria are massive, dark to 

 black rocks, traversed in aU directions by microscopic quartz-veins,, 

 so numerous that the original dark portion of the rock is now 

 divided up into small irregular patches, having a brecciated 

 appearance. In some of the microscopic sections, the areas 

 occupied by the veins are as large as those of the dark chert. The 

 groundmass of the chert is composed of cryptocrystalline silica, with 

 much dark material, probably some compound of iron. This dark 

 substance is either evenly distributed in the rock, or it has an im- 

 perfect laminate or wavy arrangement, which seems to follow lines 

 of cleavage-pressure. The radiolaria, for the most part, are casts 

 only, without any definite bounding-walls, their outlines being. 



^ Quart. Journ. Geol. Soc. vol. xlix (1893) p. 211. 



