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84 Professor Epwarp Hutt—On the Nature and Origin of Beds of Chert. 
GENERAL CoNCLUSIONS. 
(1.) That carbonate limestone chert is essentially a pseudomorphic rock consisting 
of gelatinous silica replacing limestone of organic origin chiefly foraminiferal, cri- 
noidal, and coralline. 
(2.) That this replacement occurred locally and at intervals throughout the pe- 
riod, and during the formation of the carboniferous limestone of Ireland, but in a 
special and extensive degree at the close of the limestone period, and before the 
overlying Yoredale shales were deposited. 
(3.) That this replacement occurred under the waters of the sea itself while the 
limestone was in a more or less plastic condition, admitting the free percolation of 
water, holding silica in solution. 
(4.) That as regards the modus operandi, the phenomena may be accounted for 
upon the principles of chemical transmutation explained by Bischof and other 
physicists, and illustrated by the examples of the silicification of miocene coral 
beds of the West Indies, as described by Professor Martin Duncan. At intervals, 
during the formation of the limestone, the limestone was replaced by silica in so- 
lution. This process took place on a large scale at the close of the limestone pe- 
riod. From some cause probably connected with the elevation of the sea-bed,* 
the waters of the sea appear to have been largely charged with silica in solution, 
while the chemical process was accelerated by the warm surface waters of a shal- 
low sea, and thus the transmutation process was more effectually brought about 
than previously. . 
(5.) It does not. appear that the case of silicious sea bottoms, such as that of 
the great depths discovered by the soundings of the “Challenger” in the Southern 
Ocean, affords an example of the phenomena here described—the sea bottoms re- 
ferred to being directly due to animal organisms secreting silica, such as Diatomacee, 
Polycystinese, and the spicule or skeletons of sponges. ‘The silicious material here 
described can only be considered as a secondary product due to the replacement of 
lime carbonate by silica. 
EXPLANATIONS OF PHoToGRAPHIC SECTIONS OF OnERT, Pxate ITI. 
Fig. 1. Coralline chert, from Knock-na-Rea, County Sligo, described No. 4, p. 48, mag. 3 diams. 
», 2. Black compact chert, from Benachlan, Florence Court, County Fermanagh, described No. 5, 
p- 48, mag. about 15 diams. 
», 3. Dark compact chert, from Ballymote, County Sligo, described No. 1, p. 48, mag. about 10 
diams. 
» 4. Brownish mottled and band chert, from Ballymote, County Sligo, described No. 2, p. 48, mag. 
about 10 diams. 
», 9. Black compact chert, from Knocknarea, County Sligo, described No. 4, p. 48, mag. about 10 
diams. 
» 6. Dark compact calcareous chert from Florence Court Park, County Fermanagh, described No. 
9, p- 49. This section exhibits the structure of the original limestone, in a transitional 
condition between limestone and chert, as shown by Mr. Hardman’s analysis (No. IX), 
mag. about 19 diams. 
* See Mr. Hardman’s remarks. 
