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THK MAGNESIAN LIMESTONE OF THE CORK 



DISTRICT. 



BY THOMAS FARRINGTON, M.A., F.C.S., F.I.C. 



[Read before the Cork Naturalists' Field Club, March 15th, 1893. J 



The beds of dolomite, or magnesian limestone, existing in 

 the neighbourhood of Cork, though inextensive, are not alone 

 important in connection with our local manufacturing indus- 

 tries, but as having also considerable interest from a geological 

 point of view. Almost the whole surface of the county is oc- 

 cupied b}^ the various subdivisions of two formations, viz., the 

 Old Red Sandstone and the Carboniferous limestone ; anything, 

 therefore, that opens the door for a wider study of the 

 science ought to be welcome to its students here. 



The presence of dolomite, in association with the Cork lime- 

 stone, has been somewhat of a puzzle to geologists, and one 

 eminent exponent of the science, Professor Harkness, has at- 

 tributed its origin to the action of sea-water upon the ordinary 

 limestone. In a paper on "Jointing," read before the Geo- 

 logical Society of lyondon, June 9th, 1858, he says : — 



" The mode in which the magnesian limestones make their appearance 

 in the district under review leads to the inference, that the dolomites 

 were not deposited by the ordinary action of water as sedimentary rocks, 

 but that they are superinduced structures, which have not only arisen 

 from the action of forces operating subsequent to the deposition and con- 

 solidation of the limestones in which they occur, but have had their 

 origin after the operation of that force which has produced joints among 

 these limestone strata.'" 



The object of the present communication is to adduce some 

 facts which seem inconsistent with a portion of this statement, 

 and to bring forward another theory which seems to accord 

 better with all the facts of the case. As the greater part of the 

 above quotation fits in as well with this latter theory as with 

 the Professor's own, the only portion of it directly traversed is 

 that which asserts " that the dolomites were not deposited by 

 the ordinary action of water as sedimentary rocks, but that 

 they are superinduced structures." So far from confirming 

 this view, my observations have led me to an opposite con- 



1 Quarterly Journal Gcol. Soc, London^ vol. xv. (1859), p. lOO. 



