210 STRATIGEAPHICAL GEOLOGY 



almost entirely of marine origin, and are really comparable with 

 the Devonian Series of these more southern areas. 



The upward passage from Silurian to Devonian is exhibited 

 in the coast section of the Dingle promontory in Kerry, where the 

 beds with Ludlow fossils are conformably overlain by grey, brown, 

 and purple slates without fossils, followed by alternations of grey 

 grits and slates, the grits at length predominating and forming a 

 thick series of hard, massive green and purple grits. 5 The whole 

 of this Gritstone Series is perhaps 8000 feet thick, and is succeeded 

 by slates of red and purple tints, with beds of conglomerate at 

 Parkmore, which curiously enough enclose pebbles containing 

 Silurian fossils. No other fossils have yet been found, and except 

 for the occurrence of these derived pebbles, the whole of these 

 slates and grits might be taken for a continuation of the Silurian 

 rocks, so similar are they to the underlying fossiliferous series. 



A similar set of green and purple grits occupies large areas to 

 the south and south-west of Dingle Bay in the Inveragh and 

 Dunkerron promontories, and in the districts of Killarney, 

 Kenmare, and Glengarriff. It has generally been assumed that 

 these " Glengarriff Beds " are the equivalents of the Dingle Beds, 

 but Jukes was doubtful on the point, and Mr. M'Henry is of 

 opinion that the latter are entirely below the Glengarriff Beds. 

 It is possible, however, that the actual base of the latter does occur 

 in the Dingle promontory. 



The great series known as the Glengarriff Grits consists of 

 several thousand feet of alternating bands of fine-grained grit and 

 slate. The lower part is mainly composed of green grits with 

 subordinate beds of slate ; while in the higher part purplish-red 

 slates predominate over the grits. No minor subdivisions have 

 yet been made, and no fossils have been found in them. The 

 thickness of the whole series has been roughly estimated at 8000 

 feet, but when allowance is made for folds and faults it may prove 

 to be much less than this figure. 6 



The beds have been subjected to such pressures that the shales 

 are cleaved into slates, and the grits rendered nearly as hard as 

 quartzites. They have also been thrown into a succession of 

 regular anticlinal and synclinal folds which range east and west 

 from the west coast of Kerry to the eastern part of Cork. The 

 hard grits of the lower series, though exposed in anticlines, form 

 long ranges of mountains because of their capacity for resisting 

 subaerial erosion, while deep longitudinal valleys have been 

 excavated through the purple slates and the still softer black slates 

 which overlie them and come into the synclines (see map, Fig. 94, 

 and section, Fig. 72). 



