E. T. Sarclman — White Chalk of Tyrone. 43o 



By the kind permission of Prof. Galloway the quantitative analysis 

 was made in the laboratory of the Eoyal College of Science, Dublin. 



As the potash and soda were very small in quantity, it was not 

 worth while to estimate them, and the residue insoluble in hydrochloric 

 acid, amounting to but 1-565 grains in 297*5 of the limestone, was 

 considered to be silica, being too small to analyze. 



There is nothing remarkable about the other constituents, except 

 the presence of zinc, which I believe it is unusual to find dissemin- 

 ated in an invisible form over a large extent of rock, even in trifling 

 local amount. At any rate I have never seen it given in such 

 analyses as I have met with, of limestone or other rock, — although its 

 ores are known to be often associated with the former ; but for the 

 most part as subsequent deposits in cavities of erosion. 



I happened to discover its presence in the Chalk accidentally, while 

 examining it in the wet way for titanic acid, which I imagined might 

 be expected to result from the decomposition of titano-ferrite in the 

 overlying basalt. The titanic acid did not reveal itself, but a strong 

 indication of zinc appeared. I then determined to test it in the dry 

 way, and on fusing some of the powdered chalk with carbonate of 

 soda on charcoal, I was able actually to reduce a small portion of the 

 metal so as to obtain a few spangles of it. These, when subjected to 

 the proper tests, gave the usual re-actions with the blow-pipe which 

 characterize zinc compounds. I repeated this experiment several 

 times with different speciiuens of the Chalk, and was able to satisfy 

 myself fully of the presence of the metal in it. 



As from some of these trials zinc appeared to be in such quantities 

 that it might be estimated, 297-5 grains of the powdered chalk were 

 taken, dissolved in hydrochloric acid, ti-eated with sulphuretted 

 hydrogen, in the expectation that some of the metals precipitable by 

 it were present; silica, iron, and alumina were removed, and it was 

 finally examined for zinc. This was unmistakably proved to be 

 present, but unfortunately in too small a quantity to weigh. In fact 

 it appears to be unequally disseminated throughout the rock, for 

 ■while in some very small portions siibmitted to qualitative analysis 

 it was extremely perceptible, yet in the large quantity above named 

 it seemed disproportionately small. 



It thus became a question whether the metal occurred merely 

 locally, or was widely scattered over a large area of the Cliallc. I 

 therefore examined a specimen of hard white chalk from Slieve 

 Gallion Carn, in the Co. Derry, some eight miles, as the crow flies, 

 north-west of Legmurn. It occurs there as an outlier on the New Eed 

 Sandstone, and underlies the basalt. The specimens obtained here 

 lay but two feet below the basalt, but could not be distinguished in 

 appearance from the others, which were taken at some distance from 

 the edge of the dolerite. It contained a few slightly reddened flints 

 however. The examination was only made for zinc, and was done 

 as before, by fusing a portion with carbonate of soda before the 

 blow-pipe.' As was expected, tlie metal was here also reduced, and 



1 Fletcher's hot-blast gas blow-pipe was used, and by its means a comparatively 

 large quantity of the powdered chalk and of the basalt (see jjosl) could be treated. 



