Hardman — On the Carboniferous Dolomites of Ireland. 721 



is nowhere so abundant in surface-waters as some writers on this 

 subject apparently consider, and that we are justified in rejecting 

 the statement that most dolomites are formed by infiltration of mag- 

 nesian water, at least until more evidence on that head is produced. 



It would appear, in fact, to be more reasonable to assume that the 

 lime in limestone rocks was conveyed into them by percolation 

 of mineral waters, than that the magnesia of dolomitic rocks so 

 originated. 



A. very important paper bearing on this subject, and perhaps the 

 only one in which it has yet been definitely treated, is that of E. 

 V. Gorup-Besanez, on the Dolomite Springs of the Jura."^* The author 

 gives a series of analyses of waters of springs rising in the Jura, many 

 of them in the neighbourhood of, or as it would appear, actually rising 

 from, dolomitic limestones ; and he finds that in some cases the car- 

 bonate of lime, and of magnesia, are actually present in dolomitic pro- 

 portions. Por instance, two springs give the following — 





I. 



II. 



Ca CO3, . 



. . r)7-32 



57-21 t 



Mg CO3, . 



. . 42-68 



42-79 



This is very remarkable indeed. 



Some of the analyses gave, however, the following 



Ca CO3, 

 Mg CO3, 



12 



89 

 11 



70 

 30 



68 

 32 



and the mean of the analyses was — 



Ca CO3, 

 3d"ff CO3 



53-71 

 14-29 



The author is led to agree, therefore, with Bischof in the opinion 

 that, from perfectly formed dolomites, water containing carbonic acid 

 dissolves out Ca C03 and Mg C03 together in fixed proportions,:]: but 

 does not coincide with him in the idea that the presence of magnesite 

 in cavities of the magnesian limestone prove the dolomite to be a per- 

 fectly formed one,§ since crystalline magnesite would not be deposited 

 from such solutions. He considers the geological formation of dolo- 

 mite a subject yet quite unsettled, and is opposed to Bischof 's admission 



* Ann. Chem. Pharm. Suppl. Band, viii., 230-242. Abs. Jour. Chem. Soc, vol. 

 X., p. 59. 



t In aU tte analyses, other constituents proved too trifling for notice. 

 % See Bischof, Chem. Geol. iii., p. 196. 

 § See Bischof, op. cit., hi., p. 196. 



3U2 



