438 Dr. G. J. Hinde — Organic Origin of Chert. 



Hull had clear evidence in his own possession ; that its nature had 

 been publicly pointed out by Prof. Sollas ; and that he has entirely 

 ignored it in his reply to my statement. 



As I have been engaged during this last year in an investigation 

 of the character of the Carboniferous Chert of Yorkshire and North 

 Wales, which proves to be unequivocally of the same organic 

 nature as the Chert in the Cretaceous strata of the South of England, 

 this emphatic denial of the organic origin of the Carboniferous 

 Chert in Ireland by the Director of the Irish Geological Survey 

 made me desirous of examining for myself the character of the 

 rock in question, and with this end in view, I visited during this 

 last July the various localities in Ireland in which, according to 

 Prof. Hull, the Chert in the Carboniferous series is best developed, 

 and I propose now to give a short notice of the observations I made 

 in the field, and also of a microscopic examination of the specimens 

 I collected. Time has not allowed me to work out fully the results 

 of my studies of the English and Welsh Carboniferous Chert, and I 

 shall only make a brief i-eference to these rocks at present ; but the 

 specimens I have brought will enable any one to see how close is 

 the resemblance in general characters between the same rock from 

 the different countries. 



Before starting on my search, I called at the Office of the Geolo- 

 gical Survey in Dublin, and through the courtesy of Prof. Hull, 

 for which I tender him my best thanks, I was allowed to examine 

 under the microscope the series of sections of Carboniferous Chert 

 prepared for his original description of the rock, including the two, 

 in which, according to Prof. Sollas, sponge-spicules make up the 

 larger part of the Chert. I can fully substantiate this statement 

 of Prof. Sollas, not only as regards the specimens which he examined, 

 but in others as well ; the sponge-spicules in the slides are mostly 

 shown in transverse section and their characters are unmistakeable. 



It is somewhat strange that with specimens filled with sponge- 

 spicules before him Prof. Hull should not in his paper have made 

 a single mention of these structures beyond denying that they had 

 anything to do with the structure of the rock. If we compare the 

 original specimens with the descriptions given of them, the mistake 

 made by Prof. Hull is at once apparent. Thus, for example, the 

 section of the brownish and banded Chert from Ballymote, County 

 Sligo, represented on fig. 4 of the plate, is stated to contain, 

 "circular disks of crinoids, sometimes with dark central nuclei, 



attracted from the exterior medium by tlie animal matter, and not secreted from the 

 living sponge." In the original I distinctly state that the living sponge secreted 

 the silica now forming the Chert from the exterior medium [i.e. the sea-water). In 

 the quotation, Prof. Hull omits the important words '■these'' and '■by,'' and then 

 accuses me of not stating that the silica was originally derived from the sea- water ! 



Again, Prof. Hull on page 305 of his paper gives as a quotation from my paper, 

 between inverted commas, the following passage, " The beds and irregular masses of 

 Chert have been derived solely from the silica of the sponge-remains, instead of 

 from that held in solution by the sea- waters themselves." This passage, quoted as 

 a verbatim extract, does not occur in my paper, and is not even a fair representation 

 of my meaning, which will be seen by turning to pages 432, 3, to be, that the silica 

 of the Chert was not derived directly from that held in solution in the sea-water. 



