76 EEOORDS OF THE AUSTRALIAN MITSETJM. 



of calcium from corals, shells, etc., and deposited silica in its 

 room, a portion of the calcium compound also being rearranged 

 and re-precipitated." 



With the view of showing the size obtained by a single rosette, 

 Prof. Church figures three costse and intermediate furrows of an 

 ordinary-sized Fecten, over which it had spread. 



The best examples of Beekite in our Collection are a very large 

 Syringopora from the Siluro-Devonian Limstone of Cave Flat, 

 and a Heliolites from the Wellington Caves. In the former case 

 the whole of the corallite walls are converted into a granular 

 chalcedonic quartz arranged more or less in lines, where the 

 surface is not occupied by the Beekite rosettes, which are usually 

 contiguous to one another and touching. Each rosette consists 

 of a central nucleus, surrounded by concentric rings, which seem 

 to slightly imbricate at their edges. As a rule there are two or 

 three rings, but any number may occur up to eight. Here and 

 there, two nuclei with their rings are surrounded or enfolded in 

 larger and outer rings, forming, as it were, double rosettes. The 

 rings are not always continuous, but broken up into circlets of 

 granules ; and the more numerous the circles are, the finer and 

 closer together they become. In a few cases the rosettes appear 

 to have been so rapidly developed as to have become more or less 

 confluent, whereby the regularity of form is in a measure lost. 

 The concentric structure extends through the whole thickness of 

 the corallite walls. 



In the Heliolites two conditions are apparent. In the first, 

 tlie entire surface of the corallum, including both autopores and 

 siphonopores, is converted into a series of large rosettes, obliterat- 

 ing totally the two orders of polygonal corallites. In the second 

 case the autopores remain as more or less rounded openings, 

 the siphonoporal (" coenenchymal ") surface being occupied by 

 the rosettes, this being a species of Heliolites in which the 

 siphonopores are largely developed. 



Two well-marked instances of Beekite silicification may l)e cited 

 for comparison. Prof. James Hall has figured* a Fenestella from 

 the Upper Helderberg Formation of New York State, in which 

 the whole of the polyzoarium, both interstices and dissepiments, 

 is converted in this way. Another case is that of Dr. F. Toula's 

 figuref of Sjni-ifer striato-paradoxiis, Toula, from the Carboniferous 

 Limestone of Spitzbergen, in which the rosettes are in some 

 respects even better marked than in our specimens. 



* Ann. Eeport State Geologist of New York for 1882 [1883], No. 2, 

 t. XXXV. (28), f. 18. 



t Sitz. K. K. Akad. Wissensch. (Math. Nat. CI.), Wien, LXVIII., Abth. 

 1, t. 1, f. 2a. 



