28 GUIDE TO THE FOSSIL INVEETEBEATE ANIMALS. 
l^J^diolana from a .similar rock in Cuba, with illu.strative 
15 c ratings, is shown in Table-case 15. In these soft Cainozoic 
deposits many lladiolaria belong to species still living, and 
their skeletons are as perfect as those in modern ooze. In 
the Mesozoic and Palaeozoic rocks, howev’er, the oozes have 
been changed, by pressure, or heat, or the percolation of 
vatei, into (juartzites, cherts, and flinty shales, so different in 
appearance that their radiolarian origin has not long been 
Fig. 7. — Radiolarian rock from the Lower Culm at Carzaiitic Quarry, near 
Launceston, Cornwall. Appearance 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.) 
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 tlie skeleton. In this way Padiolaria 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 and Cornwall (Fig. 7), and 
Ordovician cherts from Cornwall and the south of Scotland. 
