JL. W. Fulcher — On the Hirnant Limestone. 115 



Tiess of the grains is due to carton in an amorphous form. The 

 following were the numbers obtained by a quantitative analysis : — 



100-83 



These figures correspond to a total percentage of CaC03^72-82, 

 MgC03r=2-2, and FeC03=2-43. It also gives off a trace of SHg when 

 dissolved in hydrochloric acid. The insoluble residue (including 

 the carbon) contains approximately carbon 7 per cent. ; Si02 77 per 

 cent.; and Fe.^Og + AI.2O3 11 per cent.; the remaining 5 per cent, 

 containing lime, etc. 



The specific gravity of the rock varies slightly in different speci- 

 mens from the same locality. Thus two determinations kindly 

 ■communicated to me by Prof. Cole gave 2-604 and 2-67, while 

 another for which I am indebted to Mr. Hume gave 2-642. These 

 differences are readily explained by the variation in composition of 

 this rock, even at distances of a few inches in the same specimen, 

 which is shown when sections are observed under the microscope. 

 Eeference is made to this further on. 



When a piece of the rock is treated with dilute hydrochloric acid, 

 the calcite is gradually dissolved and the grains are left as little 

 black hollow ellipsoids, together with a quantity of fine sand and 

 carbon in powder. These black grains, when pressed by the finger 

 on a piece of paper, soil both the paper and the fingers just like 

 soot would do. Bat they are not wholly composed of carbon; for on 

 iheating them to redness in a platinum capsule, they turn of a reddish- 

 'brown colour, still retaining their shape, though all the carbon has 

 'been burnt off. It is easily seen now by applying the usual tests 

 that these residues are composed of silica coloured by a little oxide 

 of iron. Some of the black grains mounted in Canada balsam show 

 a concentric structure, but this is much better studied in sections of 

 the rock itself. 



Amongst the residue of a piece of the rock about 1^ inches square 

 I also obtained some fragments of a very fine micaceous sandstone, 

 the largest of which measured 11 X 8 mm. This particular fragment 

 also had some very regular black markings on its surface, which I 

 thought might possibly be leaf-scars ; but on submitting the frag- 

 ments to Mr. Boodle, this gentleman gave his opinion against this 

 idea, but suggested that they might possibly be aggregations of fine 

 sand around small vegetable filaments, as the carbon in the fragments 

 seemed to occupy the hollows of very small canals. Of course this 

 point cannot be settled until large quantities of the rock are dis- 

 solved, so that a good man}'- of these fragments can be examined. 



