Prof. W. J. Sollas on Sponge-spicules in Chert. 141 



XIII. — Note on the Occurrence of Sponge-spicules in Chert 

 from the Carhoniferous Limestone of Ireland. Bj Prof. 

 W. J. Sollas, M.A., F.R.S.E., &c. 



On studying the beautiful microphotographs of sections of 

 chert figured in Prof. Hull's valuable paper " on the Nature 

 and Origin of the Beds of Chert in the (Jpper Carboniferous 

 Limestone of Ireland " *, it appeared to me that in some of 

 these photographs traces of sponge-spicules could be seen. On 

 communicating mj opinion to Prof. Hull, he most obligingly 

 sent me five of his mounted sections of chert for microscopical 

 examination. For this act of kindness I now offer him my 

 best thanks. 



The results of my examination of the slices were, in the 

 first place, to completely confirm his clear descriptions of the 

 appearances presented by them, and, next, to establish the 



Fiff. 1. 



a O 

 O 



O 



o 



d 



Sections of sponge-spicules in Carboniferous chert: a, transverse ; b, longi- 

 tudinal ; c, transverse, showing axial canal ; d, showing radiately 

 crystalline structure. (Maguitied 50 diameters.) 



truth of my supposed detection of sponge-spicules. The slides 

 are numbered C 22 (fig. 4 in Prof. Hull's memoir), C 23, C 24, 

 C 25 (fig. 1 in the memoir), and C. 41. In the first four a 

 number of clear spaces with definite circular outlines (fig. 1, a) 

 O'OOS inch in diam. were clearly visible, and also a number of 

 long, straight, parallel-sided bands {I)) of the same breadth as 

 the diameter of the circles. The bands are longitudinal, the 

 circles transverse, sections of sponge-spicules, and are exactly 

 similar to those with which I am from long acquaintance 

 familiar in the flint and chert of other localities. 



The transverse sections frequently show a central dark spot 

 (c) , the remains of the axial canal ; and in both directions 

 of section a radiate crystalline structure (t/), such as I have 

 often observed and recently described in loose fossil spicules, 

 is apparent with polarized light. 



* Sci. Trans. Roy. Dublin Soc. vol. i. n. s., p. 71, pi. iii. 



Ann. & Mag. N. Hist. Ser. 5. Vol. vii. 11 



