62 The Irish Naturalist. [March, 



The Geological Structure of the Kenmare District. 



In the Irish Naturalist for January, 1899, Mr. G. H. Kinahan comments 

 on my statement that the structure of the Kenmare district " presents 

 little apparent complication." The word " apparent " was intentionally 

 introduced, to cover the possibility of faults and thrust-planes parallel 

 to the axes of folding, such as one sometimes hears of in conversation 

 with the field surveyors who have revised the older mapping. 



The region must surely remain, however, an example of classically 

 simple folding. The faults in certain places produce a repetition of 

 features ; but the broad structure is for the most part one of anticlinal 

 ridges and synclinal hollows ; the frequent overfolds cannot be said to 

 complicate this structure. The overfolds are again and again indicated 

 by the dips recorded on the Survey maps, but were often disregarded in 

 the published sections. I have recently had occasion to call attention 

 {Knowledge, vol. xxi., p. 77) to the inversion of strata that has taken 

 place. 



I do not understand the words " at Kenmare it is the reverse," in Mr. 

 Kinahan's second paragraph, since the older rocks are said to be thrust 

 over younger ones in both the cases cited. Is there really an overthrust 

 in the Kenmare synclinal, or merely an unbroken overfold ? Mr. 

 Kinahan's statement as to the absence of the Yellow Sandstone series 

 and the Lower Limestone shale on the north side is usefully suggestive 

 of a thrust-plane. 



The question of the substitution of Carboniferous Slate for the more 

 normal Carboniferous series north of it must have depended on original 

 conditions of deposition, and does not complicate the structure of the dis- 

 trict. It may be conceived that the passage from the one type of deposit 

 to the other occurred in the lost beds that have been denuded from the 

 anticlinal mass between Kenmare and Glengariff. On the original sea- 

 floor, there were at least fifteen miles in which the change of deposit 

 could have occurred. Professor Barrois, in his recent study of the 

 deposits at the mouths of the Vilaine and the Loire (" Sur les phdnomenes 

 littoraux actuels du Morbihan," Ann. de la Soc. geoL du Nord, tome xxiv., 

 p. 182), has shown how the most diverse sediments may accumulate side 

 by side on the same coast. In his special localit}-, the muds gather near 

 the shore, and escape further distribution, where the water is land-locked, 

 or where the sea-floor falls steeply from the coast. The Carboniferous 

 Slate seems to require a land-ridge or coastline somewhere to the south ; 

 but this is a question on which I cannot speak with confidence. 



Grenyii^k A. J. Coi,E. 

 Dublin. 



