558 UADIOLAItlA IX PALAEOZOIC ROCKS, 



octahedra of magnetite and cleai* or dark yellow rhomboliedra 

 of calcite. These crystals are seldom oljservable in the Silurian 

 forms, and are not visible in the Devonian. Very little other 

 organic remains are associated with the radiolaria. Only sponge 

 spicules, belonging to the Hexaetinellida^, are found associated 

 with the radiolaria, sometimes in great numbers. 



Isolated examples only of foraminifera are met with in the 

 siliceous limestone of the Muschelkalk. In the Silurian siliceous 

 shales of Langenstriegis, Rehan and Steben fragments of grapto- 

 lites and gonophores are not infre(iuent. 



Plant remains. — Prickly macrospores occur in the radiolarian 

 rocks of the Jura as well as in the Carboniferous siliceous schists 

 of the Hartz Mts. These were found in great abundance in a 

 Lower Silurian limestone from Koneprus in Bohemia, in which 

 hitherto radiolaria have not been detected. 



Another important contribution to the knowledge of Pala?ozoic 

 rixdiolaria is that by Hinde and Fox*, from which the following 

 abstracts may be made. 



Radiolaria occur at Codden Hill. The Codden Hill beds have 

 a baked appearance, are whitish, buff, or dark grey in colour, and 

 have frequently a chertoid texture, consisting of thick shales and 

 fine-grained grits. 



In places in the radiolarian chert wavellite is developed along the 

 joint planes. Sponge spicules are associated with the radiolarian 

 rock. The radiolarian series of the Culm is probably at least 200 

 ft. in thickness, if the intercalated fine shales be included. 



Individual beds usually are from 2-4 inches thick, rarely as 

 much as 1 foot. 



The beds are intersected by numerous fine and even joint 

 planes, which have the effect of dividing the rock up into com- 

 paratively small rectangular or rhombohedral fragments with 

 smooth flat surfaces. 



* Q.J.G.S. Nov. 1895, Vol. 1. G. J. Hinde and Howard Fox. " On a well 

 marked Horizon of Radiolarian Rocks in the Lower Culm Measures of 

 Devon, Cornwall, and West Somerset." 



