716 PEOP. W. J. SOLLAS ON SPONGE-SPICULES IN THE [NoV. 1 899, 



38. On the OccrRPvENCE of Sponge-spicules in the Caebonifeeous 

 Limestone of Deebyshiee. Ey Prof. W. J. Sollas, M.A., D.Sc, 

 LL.D., P.R.S., P.G.S. (Read April 12th, 1899.) 



Aftee the reading of a paper ' On the Geology of the Ashbourne 

 & Buxton Eailway,' ^ by Mr. H. H. Arnold-Bemrose, I ventured in 

 the discussion that followed to suggest doubtfully the presence of 

 sponge-spicules in one of the slices of Carboniferous Limestone that 

 were exhibited in illustration of the subject on that occasion. As 

 I had then opportunity for only a hasty glance through the micro- 

 scope, I was not able to speak with much assurance ; but through 

 the kindness of Mr. Arnold-Bemrose I have since been able to give 

 a more careful study to his preparations, and can now positively 

 affirm what I before merely suggested. The remains of sponge- 

 spicules are fairly abundant in a rock-slice taken from a specimen 

 obtained at Tissington cutting ; they present themselves as sections 

 cut in various directions, longitudinal, transverse, and oblique, 

 through long cylindrical rods, the terminations of which are obscure 

 and indefinite : in rare instances the rod exhibits a marked expansion 

 at one end, but does not assume a form that would enable us to 

 refer it to any recognized order of the sponges. The greatest length 

 observed for these spicules is 1*5 mm., the greatest diameter is 

 0*08 mm., and the least diameter is 0*027 mm. When complete they 

 were doubtless larger, but in any case they are far from approaching 

 the comparatively colossal dimensions of the spicules of Hyalosielia, 

 and rather recall such forms as have been identified by Dr. Hinde, 

 I fear on insufficient grounds, with those of the existing genus 

 Axinella.'^ The fossil species of the so-called Aoci7iella occur in the 

 Carboniferous Limestone of Clitheroe (Lancashire). 



The spicules were doubtless originally siliceous ; they are now 

 completely transformed into carbonate of lime. The replacement 

 has taken place in a very characteristic fashion ; the first stage in the 

 process is not represented in this case : for an example we may turn 

 to Hyalostelia Smithii^ in the spicules of which, particularly in in- 

 stances from the Carboniferous Limestone of South-western Scotland, 

 a rhombohedral pitting extends from all over the surface deep into 

 the substance of these bodies ; each pit is occupied by a crystal of 

 calcite, which has completed its growth within the spicule as freely 

 as outside it. The calcite, indeed, appears to have exercised a 

 corrosive action on the spicule. Nothing of the kind is observed 

 when a spicule is dissolved in caustic potash or hydrofluoric acid ; it 

 then melts away uniformly, or only yields more readily along the 

 axial canal and between the concentric coatings. The effect in the 

 case before us appears to be directly connected with the growth of 

 a crystalline solid. In commenting on the preponderant growth 

 which frequently occurs at the edges and corners of crystals, I have 

 suggested that this is readily explicable by a principle which may 



1 Quart. Journ. Geol. Soc. vol. Iv (1899) p. 237. 



2 Monogr. Palaeont. Soc. ' Brit. Foss, Spong.' pt. ii (1888) p. 145. 



