418 Reports and Proceedings — Geobgical Society of Ireland. 
REPORTS J^TsTX) P=^OCR3R]I3ITsrC3-S. 
I. — Royal Geological Society of Ikeland. — March 16, 1877. 
“On the Nature and Origin of the Beds of Chert in the Upper 
Carboniferous Limestones of Ireland.” By Prof. Edward Hüll, 
M.A., F.R.S., Director Geol. Survey of Ireland. With “ Chemical 
Notes,” by E. T. Hardman, F.C.S., Geol. Survey of Ireland. 
After reviewing what had been published by previous authors on 
the origin of chert-beds, and showing that much remained to be done 
in this department of petrology, the author proceeded to describe the 
geological position of the principal cherty zone of the Carboniferous 
Limestone of Ireland, showing that, while bands of chert occur at 
intervals throughout this formation, the highest beds immediately 
under “ The Yoredale Shales ” are especially rieh in chert, and are 
frequently entirely replaced by this mineral. In these beds coralline, 
crinoidal, and other manne forms were frequently to be recognized 
by the naked eye. Thin slices for microscopic examination, taken 
frora various localities, extending from Sligo to Carlow, also showed 
that even the most dense and compact masses of chert exliibit, under 
favourable circumstances, forms belonging to those of marine animals 
— such as corals, crinoids, foraminifera, and occasionally molluscs, 
animals which build their shells or skeletons of carbonate of lime 
rather than of silica. The siliceous paste in which these forms are 
inclosed was found to be in a gelatinous state, and the forms were 
only to be distingnished by difference in depth of shade from the 
paste, the shells or skeletons having disappeared. The Chemical 
analyses of these specimens by Mr. E. T. Hardman, F.C.S., tended 
to sliow tbat the chert-beds contain various proportions of carbonate 
of lime as well as other minerals, so that a gradation from siliceous 
limestone into pure chert might be traced. From a review of the 
whole circumstances, it appeared that the origin of the chert-beds 
was to be attributed to the replacement of the original limestone 
or calcareous “ ooze,” due to organic agency, by silica, and that the 
rock is traly a pseudomorph, a view held by several observers. 
The manner in which this replacement had been brought about 
was then touched upon. It was shown that there was reason for 
believing that at the close of the period duriug which the Carbon- 
iferous Limestone was formed over the area of Central Ireland, the 
sea-bed was elevated, so as to be covered with the waters of a 
shallow sea, exposed to the sun’s rays, and of a warmer temperature 
than when at a greater depth. The waters appear to have been 
charged with a more than usual supply of silica in solution, derived 
(as Mr. Hardman suggests) from the surrounding lands, formed, for 
the most pari, of highly siliceous materials. As silica is less soluble 
than carbonate of lime, Chemical replacement would naturally take 
place, the carbonate of lime being dissolved out, and its place taken 
by the silica. The warm condition of the sea-water, its exposure to 
sunlight, the porous eharacter of the coralline, crinoidal, and other 
forms, and the soft and “ oozy ” condition of the foraminiferal mud 
would give easy access to the sea-waters, and the process of silicifi- 
