1866.] JUKES — OLD RED SANDSTONE AND DEVONIAN. 345 



same formation as that of Waterford. In like manner any one who 

 studied only the Carboniferous Slate about Cork Harbour, or even 

 about Kinsale, might look upon the Coomhola Grit portion of that 

 group in Bantry Bay, and in the western Headlands of Cork, as 

 something wholly different. 



I can speak from personal experience on this point, as I myself 

 made mistakes when first mapping the rocks of Bantry Bay, trusting 

 to the ideas gained about Cork Harbour. The identity of the rather 

 dissimilar rocks in different parts of the country came out as the 

 final result only of the Survey, when the beds had been patiently laid 

 down on the six-inch maps (in the course of several years' labour), 

 entering on those maps merely the data shown in each locality as it 

 was passed through. The monotony of this task can scarcely be 

 understood by amateur geologists, who are at liberty to select 

 their localities and pick out the more interesting and important bits. 

 Its value, however, becomes understood on its completion, when the 

 results are gathered from a mass of data collected by different ob- 

 servers working independently without any foregone conclusions to 

 vitiate their observations. 



14. General Conclusions on the Roclcs of the South-west of Ireland. — 

 One general conclusion may be briefly stated as the result of the ex- 

 amination of the western part of the county Cork, namely, that there 

 are two great formations in it, the Old Red Sandstone below, and the 

 Carboniferous Slate above ; the Old Eed Sandstone containing no 

 marine fossils and scarcely any fossils at all, except plants in its 

 upper portion; the Carboniferous Slate containing some of these 

 plants, but also marine fossils, sometimes in great profusion. The 

 Old Red Sandstone has a prevailing red tinge throughout, with no 

 beds of black or bluish-grey slate; the Carboniferous Slate has a 

 prevailing black or bluish-grey colour, with no beds of a red tinge. 

 Both are greatly affected by slaty cleavage. 



It may also be stated that where the Carboniferous Slate and Car- 

 boniferous Limestone are both present together, the Carboniferous 

 Limestone is uppermost; but that where the Carboniferous Limestone 

 has a thickness of 2000 feet, or upwards, the dark slates between it 

 and the Old Red Sandstone are very thin, rarely more than 200 feet 

 in thickness ; while where these dark slates thicken out to more than 

 2000 feet, there is no great thickness of Carboniferous Limestone over 

 them. Where the Carboniferous Slate attains a still greater thick- 

 ness, and swells out to three, four, or five thousand feet, it has never 

 any Carboniferous Limestone over it at all, but there appear here 

 and there patches of black slate upon it, which both lithologically 

 and palseontologicaUy resemble the Coal-measures. If so, the Car- 

 boniferous Slate occupies, there, the whole interval between the top 

 of the Old Red Sandstone and the base of the Coal-measures, with a 

 perfectly conformable and continuous series of beds to the exclusion 

 of the Carboniferous Limestone; and therefore replaces that 

 Limestone. Dark grey mud and sand were at first deposited over 

 the whole area, but were subsequently restricted to a part of it, 

 where they continued to be deposited in great quantity ; while in the 



VOL. XXII. — PART I. 2 b 



