the carboniferous-limestone sekies at clifton. 191 



Middle Limestones. 



i. Oolitic Limestones at the base. 



By far the greater proportion of the residues consists of well- 

 rolled detrital quartz-grains, averaging -008 of an inch in diameter, 

 but occurring as large as '013 of an inch. A fragment of felspar 

 and some tourmaline. 



ii . MitclieTcleania-Beds. 



No. 1. A few detrital quartz-grains and a quantity of chalcedonic 

 silica. 



No. 2. Detrital quartz, averaging about '003 of an inch in dia- 

 meter, around some of which a slight secondary deposit of silica 

 has commenced. 



No. 3. Chiefly flakes of chalcedonic silica. 



No. 4. Mostly chalcedonic silica, well-rounded grains of detrital 

 quartz, as large as -Oil of an inch in diameter, tourmaline, and 

 zircon. The chalcedonic silica occurs in the form of fragmentary 

 pieces, and also as circular objects which average about -01)4 of an 

 inch in diameter, but some are considerably larger. Some of these 

 objects are isolated, but in other instances two or three are seen 

 attached together. A reference to a thin section of the rock shows 

 that the structure is much obliterated, but that the limestone is 

 made up of calcareous circular bodies. Some of these are concre- 

 tions, with Foraminifera as nuclei ; but others are definite organisms, 

 and correspond with the chalcedonic objects in the residue. As to 

 what these" organisms are, does not enter into the province of this 

 paper ; it is enough for us to know that the circular forms in the 

 residue are casts or pseudomorphs of the calcareous objects which 

 form the limestone. 



iii. Main Portion of the Middle Series. 



No. 1. Earthy brown limestone. Plakes of amorphous and chal- 

 cedonic silica, apparently associated with organic matter. 



No. 2. Dark siliceous masses, mixed with organic matter. To 

 test this, the organic matter was estimated and found to be 12*8 

 per cent, of the rock. It may be M^ell just to mention that the 

 structure of the rock at this horizon is much obliterated, which 

 may be due to the action of organic acids given off from organic 

 matter. If we allow for loss by decomposition, the proportion of 

 organic matter originally present in the limestone must have been 

 considerable. 



No. 3. Detrital quartz and a quantity of chalcedonic silica. 

 Seen by reflected light, the latter appears as dark-brown and snow- 

 white objects. Pyrites plentiful, in the form of minute balls, 

 measuring '002 of an inch in diameter, and also apparently as 

 pseudomorphs of organic structure. In some cases the dark 

 appearance of the chalcedonic silica is due to the admixture of 

 pyrites. 



