28 GUIDE TO THE FOSSIL INVEKTEBEATE ANIMALS. 



Gallery X. 400 species have been described ; and a glass slide with 

 "^^^15"^^^^ Eadiolaria from a similar rock in Cuba, with illustrative 

 drawings, is shown in Table-case 15. In these soft Cainozoic 

 deposits many Eadiolaria belong to species still living, and 

 their skeletons are as perfect as those in modern ooze. In 

 the Mesozoic and Palaeozoic rocks, however, the oozes have 

 been changed, by pressure, or heat, or the percolation of 

 water, into quartzites, cherts, and flinty shales, so different in 

 appearance that it is not long since their radiolarian origin 



Fig. 7. — Radiolarian rock from the Lower Culm at Carzantic Quarry, near 

 Launceston, Cornwall. Photograph of a thin section as seen under 

 the microscope. Enlarged about 32 diameters. (From paper by 

 Hinde and Fox in the " Quarterly Journal of the Geological Society," 

 ' ' \ ' vol. li ; by permission of the Council.) (See Table-case 15.) 



was discovered. This was done by examining thin sections 

 of the rock under the microscope, when in some, less altered 

 than most, the skeletons were recognised. Usually, however, 

 the skeletons themselves have been dissolved, and there can 

 only be detected spots of transparent silica formerly deposited 

 in the cavity of the skeleton. In this way Eadiolaria have 

 been found in siliceous rocks as far back as to the Cambrian 

 period. In illustration of this are exhibited specimens of the 

 Table-case radiolarian chert and shale of Carboniferous age, found in 

 the Lower Culm of Devonshire aud Cornwall (Fig. 7), and 



