30 PROTOZOA. RADIOLARIA 



smaller than later forms of the group, and are thought by 

 some authors to be simply inorganic aggregations. 



In Britain the earliest examples of the Radiolaria 

 occur in the Ordovician rocks of the south of Scotland, 

 where they form beds of chert ; others which are perhaps 

 of nearly the same age, have been found in a chert from 

 Mullion Island (off the west coast of the Lizard). A few 

 specimens have been noticed in the Carboniferous Lime- 

 stone of Flintshire, whilst in the Lower Culm of Devon 

 and Cornwall these organisms contribute largely to the 

 formation of thick beds of siliceous rock (cherts, etc.). At 

 several localities on *the continent Radiolaria are fairly 

 common in the Mesozoic formations, but in England only 

 a few have been recorded from the Lias, the Lower Green- 

 sand, the Upper Greensand, the Cambridge Greensand, 

 and the Chalk. In the Tertiary some have been obtained 

 from the London Clay of Sheppey. A very important 

 Radiolarian formation of late Tertiary age covers large 

 areas in the Island of Barbados, and is known as the 

 ' Barbados Earth ' ; it resembles very closely the modern 

 Radiolarian ooze mentioned above, and is probably a deep- 

 sea deposit. 



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