to the Mineral Structure of the South of Ireland. 163 



the same geological position, and presenting the same mineral 

 character and composition (as in the Monavonllagh and Knock- 

 mildown mountains, and other portions of the counties of 

 Waterford, Cork and Kerry) were coloured as belonging to 

 the upper portion of the transition series. The investigation 

 which led to this change having been very extensive and 

 minute, enabled me to make numerous corrections in the detail 

 of the outlines of the rock districts throughout the southern 

 counties, and I think it right firmly to assert that every one 

 of those subdivisions to which Mr. Weaver has applied the 

 term gratuitous, has been the result of careful observations 

 laid down on the spot, on a map on a large scale. Whether 

 the subdivisions of the strata I have made may or may not 

 eventually be considered as indicative of the boundary of 

 distinct formations, still they will be valuable as indicating 

 the boundaries of different rocks presenting distinct mineral 

 characters and fossil remains. Thus, in my map and sections 

 I have endeavoured to represent with accuracy the relative 

 positions of the several rocks as they occur in geological se- 

 quence, and when a more correct nomenclature shall be esta- 

 blished, it can be applied to both without difficulty and with- 

 out altering a single line. 



Mr. Greenough, in his introductory memoir to the new 

 edition of his geological map of England, has classed the old 

 red sandstone with the graywacke formation, and has quoted 

 from Dr. M'Culloch's System of Geology, the characters 

 of the formation as exhibited in Scotland, which he thinks 

 are equally just when applied to the west of England, and in 

 my opinion correspond very accurately with those of Ireland, 

 particularly of the south ; but I still adhere to the propriety 

 of separating these strata from the transition class on account 

 of their almost universal unconformability*, which forms a 

 stronger line of distinction between the transition slate and 

 the old red series than we find between the old red and the 

 strata which succeed it, where no unconformability is ob- 

 served, each suite, in the ascending series, succeeding the 

 other in regular succession without any break, as far up at 

 least as the new red sandstone ; consequently, there is really 

 more difficulty in determining the line between the old red 

 sandstone and the carboniferous limestone series, than between 

 it and the transition slate j\ 



* The only examples of conformability that I am acquainted with, occur 

 in the west of the counties of Cork and Kerry. See paper by me in the 

 Lond. and Ed. Phil. Mag. for March last, pp. 161—175 



t The lower beds of the carboniferous limestone in many parts of Ire- 

 land, alternate with yellowish gray sandstone, which graduate into old 

 red. 



M2 



