BY T. W. EDC4EW0RTH DAVID AND WALTER HOWCHIN. 575 



not spherulites nor oolitic granules, is rendered pi'obable by the 

 following facts : — 



(1). In the Pre-Camljrian oolitic limestone of Hallett's Cove 

 the nuclei of the grains are shaped irregularly, whereas the small 

 translucent bodies inside the nebulous rings in the Brighton lime- 

 stone are j^erfectly round or oval, and in some cases spinous. 



(2). Distinct l:)lack netted material envelopes the spherical or 

 oval bodies. 



(3). The translucent material enclosed inside the rings does not 

 show a dark cross, seen in polarised light, though, even if it did, 

 this would not of course be an insupei-able objection to its 

 radiolarian origin. It proves, howe^■er, conclusively that they 

 are not spherulites. 



(4). They. are probably not oolitic grains, not only on account 

 of many of them possessing an external black network, but also 

 because they are of exactly the same shape, size, and structure 

 as similar bodies in the Pre-Cambrian cherts of Crystal Brook, 

 and oolitic structure, as far as we know, has not been observed in 

 cherts. 



(5). Many of the casts very closely resemble those of MuUion 

 Island, Cornwall, and those of the Jenolan Caves and of Bingera 

 in New South Wales. 



A considerable variety of forms appear to be present, most of 

 which seem to belong to the Legion Spuindlaria. 



Figs. 5-6 of PL XXXIX. exhibit forms resembling (Jarposphcera, or 

 possibly Cenosphcera with the internal cavity partly filled with 

 chalcedony. 



Fig. 7 of PI. xxxjx. is suggestive of the genus Cenellipsis. 

 It is possible, however, that the netted forms like those in the 

 figures last referred to, are of inorganic origin, the p3M"ites filling 

 in the interspaces between small cr3rstalline aggregates partly of 

 silica, partly of calcite. 



The spherical chalcedonic bodies, surrounded by the outer 

 chalcedonic rings, appear to us, however, to be very probably casts 

 of the medullary and cortical shells of radiolaria. The diameters 

 of these bodies vary from -1 mm. up to '22 mm. 



