1866.] JUKES OLD KED SANDSTONE AND DEVONIAN. 333 



ments of plants in the uppermost beds, and some very obscure 

 impressions that might be those of plants lower down in the beds 

 near the Lakes of Killarney. 



A curious track, also, in some purple slates near Valencia Island, 

 was discovered by Mr. Kinahan. It seems to be such a row of 

 minute indentations as might be made by the claws of some 

 Crustacean. (See Explanation of Sheet 182, &c., p. 11.) 



The uppermost part of this great series of reddish and brownish 

 rocks is more brightly and variously coloured than the lower portion ; 

 lilac- coloured slates occurring there more fi-equently than elsewhere, 

 while the peculiar kind of massive sandstone, which acquired the 

 name of Glengarriff Grit with us, is more abundant lower down. 

 The yellow sandstones and greenish slates which characterize the 

 top of the Old Eed in Waterford pass into harder and slatier grits 

 further west, and purple slates make a greater figure among them ; 

 though these are by no means absent to the eastward, as may be 

 seen in the hills south of Clonmel. Throughout the whole region, 

 from the south side of Dungarvan Harbour to the extremities of the 

 peninsulas south of Dingle Bay, there is hardly a trace of conglo- 

 merate in this Old Red Sandstone, the whole being essentially a 

 clay-slate formation, with great groups of sandstone distributed 

 through it. 



6. The Lower Limestone Shale of the Youghal and Ardmore, and 

 the Gorh and Midleton Troughs. — In fig. 5 and its explanation it is 

 shown that the lowest margin of the Carboniferous Limestone and 

 the top of the Old Eed Sandstone are thicker at Clonea than at 

 Waterford. A still greater development of these shales and the 

 sandstones associated with them is apparent in the sections about 

 Ardmore* and Whiting Bay, and near Youghal. 



In the quarries immediately north of the latter town the thick 

 dark-grey and brown sandstones are well shown, some of them 

 having rippled surfaces, others showing impressions of large plants 

 several inches across. Many of these beds were originally calca- 

 reous, and now are externally converted into rotten-stone. The 

 dip in this locality is 70° north, and the group of shales and sand- 

 stones between the red beds and the limestone appears to be 

 500 yards wide, which would give a thickness of 1400 feet if the 



^ While going first through this district I made the mistake of looking on 

 the uppermost thick bed of coarse sandstone as the top of the Old Red Sand- 

 stone, and thus assigned too high a position to the base of the Carboniferous 

 shale group. The sandstones are often very similar in character through a great 

 thickness, but by disregarding them and looking solely to the characters of the 

 shales and slates interstratified with them, we hit on a natural boundary. As 

 long as, in descending from the limestone, these sliales or slates preserve their 

 grey or black colours, marine fossils will often be found both in slates and sand- 

 stones ; on the other hand, as long as, in ascending in the Old Red Sandstone, 

 the shales or slates show bright-red colours, no marine fossils will be found in 

 either. The instances of any alternation of red and grey slates are very few, even 

 if they really exist at all, so that in an ascending section the first black slates, in 

 a descending one the first red or purple slates, will give the boundary between 

 the Carboniferous series and the Old Red Sandstone with great approximate 



