Radiolaria. 



129 



Radiolaria are all marine ; many of them live near the surface OALLEKY 

 in tropical seas, and their skeletons sink to the bottom of the ^• 

 ocean, where they are now forming extensive deposits of ^T^iJ"* 

 radiolarian ooze at depths of from 2000 to 4000 fathoms. case 16. 



Until very lately fossil remains of Radiolaria were only known 

 from soft siliceous marls and shales of Tertiary age which occur in 

 Barbados, Cuba, Trinidad, Richmond in Virginia, Sicily, and the 

 Nicobar Islands. The Radiolaria in these deposits retain the glassy 

 silica of their shells, and for the most part they are in as perfect 

 condition as recent forms, and many are of the same species as 

 those now living. Prom these soft deposits, usually of a white 



Fig. 180 —Fossil Radiolaria. (1) Staurolonche macracantha, Eiist ; from the 

 Carboniferous of Sicily. (2) Theodiscus convexus, Eiist ; from the Carbon- 

 iferous of the Ilarz. (3) Lithostrohus Wendlandi, Eiist; Carboniteroua, 

 Sicily. (4) Cenosphcera macropora, Eiist ; Silurian, Cabneres.— All largely 

 magnified. (After Eiist.) 



chalky-looking rock, the tests may be obtained by washing. A 

 large block of this radiolarian rock from Barbados is shown in 

 Wall-case 9, and some of the Radiolaria from it are on a glass 

 slide. 



It has recently been ascertained, moreover, that Radiolana 

 may be of great geological age, and that they occur in 

 siliceous rocks of all formations from the Cambrian upwards. 

 They have been found in Cambrian strata in Thunngia; in dark 

 or reddish cherts of Ordovician age in the South of Scotland, 

 specimens and sections of which are exhibited in Table-case 16; 

 also, of probably the same age, in Cornwall; in siliceous shales at 



