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MAGNESIAN UMESTONE 

 IN THE NEIGHBOURHOOD OF CORK. 



BY JAMES PORTER, B.K- 



[At the Meeting of the Cork Naturalists' Fiekl Chib, before which 

 Mr. Farrington read his paper on the above, Professor Hartog suggested 

 that the criticisms of the writer should be embodied in the present com- 

 munication.] 



Those who are acquainted with the state of geological science 

 will not consider it remarkable that the revolutionary views 

 put forward by Mr. Farrington in the May number of the 

 Irish Naturalist should be promptly' challenged. If geological 

 problems could be solved independentl}'-, without taking into 

 account their mutual bearings, his theory might be accepted ; 

 but as things are, I believe we must contintie to regard our 

 Cork dolomite as simply altered Carboniferous limestone. 



Of the seven propositions which Mr. Farrington lays down 

 as inconsistent with the theory of Harkness, I cannot see the 

 adverse bearing of more than one, which refers to the abrupt- 

 ness of the change from limestone to dolomite. But the Cork 

 examples cannot be looked at b}' themselves in this way. 

 There are numerous instances of transitions as abrupt as any 

 to be found in Cork, in districts where the evidence of pseu- 

 domorphic origin in the case of the dolomite, is too complete 

 to leave any room for doubt. Professor Cole informs me that 

 such instances are frequent in Co. Dublin ; and the expression 

 "vertical dyke-like masses," used in the Geological Survey 

 memoir to describe some portions of the pseudomorphic lime- 

 stone near Mallow, would apply equally well to the aspect of 

 those magnesian deposits whose origin is under discussion. 



Most geologists will regard the fact stated by Mr. Farrington 

 that " the dolomite is generally less pure than the limestone," 

 as a pretty clear indication that the magnesian bands mark the 

 course formerly taken by underground water, which carried with 

 it the products of its action on the overlying rocks, including 

 ferruginous and other impurities as well as magnesia itself. 

 If, instead of the expression of Mr. Farrington, "nearly fifty 

 per cent, more foreign matter," we use his figures of 2.5 for 

 the dolomite and 1.7 for the limestone as the percentage of 



