80 Professor Epwarp Huri—On the Natwie and Origin of Beds of Chert. 
Description of Specimens.—The following is a brief account of the appearance 
of the microscopic sections of chert, which were very carefully prepaid by Mr. 
Cuttell, of London :— 
No. 1. From Upper Limestone, Ballymote, county Sligo.—Dark compact chert, 
without visible organic structure under the naked eye; under microscope shows 
wavy bands and obscure structures, some clearly organic, consisting of coralline 
and crinoidal fragments. A few veins of calcite are observable traversing the 
field of view. 
No. 2. Specimen from same district as No. 1.—Brownish mottled slightly banded, 
organic forms in irregular layers; circular disks of crinoids, sometimes with dark 
central nuclei; obscure forms of foraminifers in section, coralline structures(?) and 
bivalves (brachiopods) with crystalline silica in interiors; numerous black grains, 
‘some angular octohedrons, probably crystals of pyrites, also minute black well- 
formed hexagons with central lucid points, probably sections of calcite with organic 
matter. The slice is traversed by veins of calcite of later date than the rock itself. 
(Mr. Hardman’s analysis, No. 1.) 
No. 3. Specimen from same district as No. 1.—Brownish mottled field of view, 
presenting numerous organic forms, many circular with dark centres (crinoidal 
stems) also bivalve shells (brachiopods) and coralline and foraminiferal forms ; 
small crystals of calcite with dark linings and lucid centres are numerous ; also, 
octohedral forms, slightly tinted, probably fluor spar.* In this specimen I also 
notice well formed black hexagons with lucid centres, of the nature of which I am 
in much doubt. Mr. Hardman suggests that they may be sections of sulphates of 
strontium and barium. (Analysis II.) 
No. 4%. Specimen of black compact chert from the Upper Limestone of Knock- 
na-Rea, county Sligo.—The original calcareous rock has, apparently in this case, been 
highly cellular and fissured, so that it is replaced largely by mammilar chalcedonic 
silica liming the interiors of the cells, and the walls of the fissures; a few obscure 
forms of crinoid stems and foraminifera(?) may be made out in the more solid 
portions, much darkened by carbonaceous matter. 
No. 4°. Specimen from same locality.—Dark chert containing corals (Lithostrotion 
affine) preserved in silica of a lighter colour. The analysis shows this to be a 
siliceous limestone, though having the appearance of chert. (Analysis III.) 
No. 5. From Upper Limestone, Benachlan, Florence Court, county Fermanagh. 
—Black and compact, with bands of dark limestone alternating with the chert. 
Under the microscope the whole field shows organic structure ; forms of foraminifera 
(Valvulina),+ section of crinoidal stems, polyzoa, and curved fragments of bivalves 
can be discerned preserved in colourless translucent silica; amongst the other 
* Mr. Hardman finds traces of fluoric acid in this specimen, hence the determination above arrived 
at. 
+ Determined by Professor Rupert Jones, F.R.s, 
