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nary light, "by its dull colouration, and very finely granular or 

 radiating fibrillar structure. This structure is still more 

 beautifully seen by polarised light. The granular and 

 fibrillar portions interlace in an irregular manner ; the latter 

 show very markedly an eccentric librillar structure, radiating 

 from many points. This structure reminds one of that of 

 sphaerulites. The appearance, on the whole, may be com- 

 pared to that of ice crystals on a window, an appearance quite 

 unusual for topaz. 



Between the aggregate of topaz are seen isolated, generally 

 small brown tin crystals,in width about 0'06 mm.; in length, 

 0T3 mm., rarely larger ones of a width of 004 mm. These 

 crystals show twin formation and a zonular structure, this 

 latter structure being evident on account of difference in 

 colour. 



To judge from one specimen among the collection, the 

 pseudo morphoses which have been described appear to have 

 taken place in clefts of a breccia of tourmalin, quarzit, and 

 slate, of which several pieces are to hand. 



The previously mentioned analogy between the formations 

 of the Schueckenstein and its surroundings and these Tas- 

 manian formations is considerably strengthened by the fact 

 that this breccia, on the whole, corresponds to that in the 

 Saxon formations described by M. Schroeder. 



The specimens before me contain angular, chiefly flat, 

 fragments of stone, about 2-J cm. in size. These consist of 

 alternate layers of a light grey and brown, or greyish-green 

 substance, of a thickness from that of paper to one of 5 mm. 

 These layers are either straight or wavy. The light-grey 

 strata show a finely granular, crystalline, shiny fracture ; the 

 more darkly-coloured strata, a more dense and duller frac- 

 ture. Prom microscopic examination it is evident that these 

 slate-like specimens contain only quartz and tourmaline ; in 

 the lighter strata there is more quartz, in the darker more 

 tourmaline. 



It is known that quartz appears sometimes in the form of 

 a more or less finely granular aggregation. On treatment 

 with Hydrofluoric acid only tourmaline remains, the quartz 

 being dissolved. The tourmaline forms very minute needles, 

 0,02 m.m. broad, 0'13 m.m. long. These needles unite to 

 form fibrillar or felt-like masses, or appear isolated in the 

 quartz. Thoroughly formed or hemi-morphous crystals I 

 have not been able to find. Not uncommonly, however, are 

 seen among the needle-like and fibrillar forms characteristic, 

 roundly triangular, transverse sections of tourmaline crystals. 



By ordinary light the colour of tourmaline is chiefly brown, 

 more rarely green, and most rarely blue. The pleochroism 

 is very strong. A structure in which there is a difference in 



