156 



Scientific Proceedings, Royal Dublin Society. 



The greater number of the samples show an oolitic stracture, 

 such as is mentioned by Portlock, only that in none of them is the 

 cement of green earth, some of this mineral being, however, present 

 on one or two of the specimens. 



It may be taken for granted that the samples forwarded are of 

 the same nature as those alluded to by Portlock. The question is, 

 Are they hydrocarbonates of lime and magnesia, as he presumes — 

 that is to say, hydrodolomite, as suggested by Mr. Egan ? 



A fair sample of one of the specimens was analysed by Mr. 

 Templeton, one of the students of the Eoyal College of Science, 

 and the following are the results : — 



100-50 



A portion of this same sample gave a density of 2-722. Hydro- 

 dolomite, according to Dana, has a density of 2-495 ; therefore, 

 neither by analysis nor by density can this mineral be described 

 as hydro-dolomite : both would make it simply carbonate of lime 

 relatively pure. 



However, the examination of the hardness showed that the 

 white oolites cut ordinary limespar ; therefore they must have a 

 hardness greater than 3. Aragonite crystals they do not cut, both 

 minerals appearing to resist about equally. The hardness of the 

 oolites may therefore be taken at 3 '5. The density, being merely 

 that of pure calcite, would seem to argue against its being arago- 

 nite ; but Naumann gives for aragonite in the aggregated form, as 

 lowest limit of density, 2*7. These oolites are, strictly speaking, 

 aggregates, and the density of 2-722 is admissible for their being 

 aragonites. On the other hand, this density excludes the assump- 

 tion of their being dolomites, the limits of density for which are 

 2-8 to 2-95. 



In order, however, to test this point, samples were submitted 

 to the action of acetic acid, which in all cases rapidly decomposed 



