lyo The Irish Naturalist. 



The specific gravity of a sample of a rock is often a test of 

 its freedom from alteration. Mr. Walker of Dundee provided 

 us twelve years ago with an instrument on the principle of the 

 steelyard, by which the specific gravity of a rock can be ac- 

 curately determined, to the second place of decimals, by two 

 operations occupying together some four or five minutes.' 

 This admirable instrument is as yet too little known outside 

 scientific laboratories. 



A knowledge of the use of the maps of the Geological Survey 

 of Ireland, reference to the published memoirs of that body, 

 and to such papers as Mr. G. H. Kinahan's " Economic Geo- 

 log3^ of Ireland,"^ assist one largely in forming a judgment as 

 to the extent of a stone at the surface, the trend of its outcrop^ 

 and its characters and utility as at present ascertained. The 

 basis for most statements regarding the building-stones of this 

 country is still, however, Wilkinson's remarkable work on the 

 "Practical Geology and Ancient Architecture of Ireland," 

 published in 1845. 



The power of determining the fundamental nature of a stone, 

 by the means hinted at above, must be applied also in the 

 selection of individual blocks. The continuous export of such 

 materials often depends upon their uniform excellence ; and 

 one badly selected mass or .slab may bring discredit upon a 

 whole quarry or even upon a county. In this matter every 

 quarry-man has an interest as great as that of the quarrj-owner 

 or the builder ; whether in blasting, excavating, or shaping, 

 each man employed should possess an intelligent knowledge of 

 the properties of the material beneath his hands. 



When, with the absolute truthfulness of scientific method 

 the qualities, the true beauties, of a stone have been ascertained, 

 it should be brought into the market by well trained travellers 

 or exhibitors, who should be able to discuss with an architect 

 the difference between a marble and a granite, or a sand.stone 

 and an oolite, a state of things which is far from being realised 

 at the present. Ireland may yet be able to mark a new era in 

 the stone-market by sending out scientific descriptions of her 

 materials, and by placing samples of them in some convenient 

 place of reference in I^ondon, with details of their current price 



'See '^oS^n^r, Geological Magazine, 1883, p. 109; and Cole, "Aids in 

 Practical Geology," p. 24. 

 ^ Proc. Royal Dublin Society, new series, vol. v., p. 372, etc, 



