THE CARBONIFEROUS-LIMESTO^'E SERIES AT CLIFTON. 



1<S0 



some of them of oolitic structure, the nuclei of the granules being 

 mostly dctrital quartz-grains and Foraminifera. Einally the lime- 

 stone disappears and becomes replaced by true Millstone Grit, which 

 yields from 97*4 to 98-39 per cent, of insoluble siliceous residue. 



The iNsoLrBLE E-esidues. 



The method adopted for procuring the residue was to place a lump 

 of the limestone in an e vapor ating-dish ; concentrated hydrochloric 

 acid was then poured into the dish, and, after a time, a little water. 

 When carbonic anhydride ceased to be evolved on the addition of 

 more acid, the solution was boiled and then allowed to cool. The 

 solution was next poured off, and the residue washed with distilled 

 water. At first the residue was transferred to a small flask and 

 again boiled with concentrated hydrochloric acid ; but examination 

 of the residues, before and after that operation, proved that this last 

 process was not required. 



To estimate the quantity of residue, typical samples were ground 

 to a fine powder in an iron mortar, and well mixed. One gramme 

 was then weighed out, boiled in a small flask with concentrated 

 hydrochloric acid, transferred to a filter, and washed with hot 

 distilled water so long as nitrate of silver produced any reaction on 

 addition to some of the washings collected in a test-tube. The 

 following table shows the percentage. 



Percentages of Insoluble Residues given in 

 ascending order. 



Lower LurESTONEs. 



Middle Limestones. 



Upper Limestoxes. 



Lower Lime- 

 stone Shales. 



Black 



Eock. 



Oolitic 

 Beds. 



Mitchel- 



Main 

 Portion. 



No Divisions. 



11-2 



1-9 



22-5 



70 



•8 



2-67 

 3-70 

 5-20 



10-6 

 10-0 

 2-3 

 2-2 

 30 

 1-1 

 22 

 1-9 

 1-4 



11-3 

 10-0 



2-5 (oolitic). 

 81-6 



In the case of the large proportion of residue in the first two 

 estimations of the main portion of the middle series, it should be 

 stated that the limestone contained an unusual proportion of organic 

 matter, and doubtless the high percentage is to some extent due to 



the ash of the organic substance. 



