G. S. Kinahan — Re-arranged Glacial Drift. 173 



bourhood of the Three-rock Mountain, it diminishing gradually to- 

 wards the S.S.W., but more rapidly towards the N.N.E.^ 



In favour of the supposition that the great altitudes of the shelly 

 deposits in the mountains at the junction of the counties of Dublin 

 and Wicklow are due to the combination of axes of elevation and 

 great faults, it may be pointed out that in the country to the N.W. 

 of these hills, if we come S.S.B. from the central plain of Ireland to 

 the Dublin and Wicklow hills, it will be found that the altitude of 

 the gravelly drift gradually increases ; while south of this mountain 

 range in the co. Wexford, according to Mr. Wyley's observations, 

 this drift is not to be found higher than the 300 feet contour line. 

 These anticlinal curves, with their accompanying faults, must be 

 more or less shifted by the more recent faults of the valley of the 

 Barrow, and of the other nearly N. and S. fissures, as west of the 

 Barrow fault the altitudes at which the shelly drift is recorded are 

 much less than those to the east. The following are the localities 

 associated with the Dublin and Wicklow hills and east of the 

 Barrow valley fault, in which shells are recorded : near Three 

 Eock Mountain 1200 feet, Eev. M. H. Close; Sugarloaf Mountain 

 600 feet. Dr. Oldham ; Bohernabreena, between 400 and 450 feet. 

 Dr. J. E. Kinahan; Telegraph-hill, Killiney, 400 feet. Dr. Oldham; 

 and at Naas, 380 feet. Dr. Oldham. West of the Barrow valley 

 fault shelly drifts are' only recorded in two places, both by Dr. 

 Oldham, one in the range of hills immediately west of the 

 fault, " on the flanks of the elevated coal-field, between Athy 

 and Castlecomer" [height not given], and the other on the N.W. of 

 the Slieve Bloom range at Eoscrea, co. Tipperary, at a height of 

 400 feet. 



In conclusion, I would wish to draw attention to the fossiliferous 

 drifts that in places have been found under glacial drift, and have 

 been called by me in previous writings " Pre-glacial drift." [Mem, 

 Geol. Survey, Ex. Sheets 115 and 116, page 28; Gteol. Mag. Oct. 

 1865.] These are indeed to a certain extent pre-glacial, as they 

 occur under glacial drift ; but it apjDears probable that they would be 

 more correctly spoken of as Intraglacial beds, being older than a 

 portion at least of the Moraine drift of the adjacent height, but 

 newer than the Boulder-clay drift of the central plain of Ireland. 

 This drift at present seems to be only recorded in three places, 

 namely, Boleyneendorrish river valley, adjacent to Gort, co. Gal way, 

 where it was observed by myself ; in a pit at the Newtown colliery, 

 Queen's co., where it was discovered by Mr. B. B. Edge, of Clonbrock 

 Ho ; and near Nenagh, co. Tipperary, where it was recorded by Mr. 

 Wilkinson ; the lignyte and associated beds at Lough Neagh, cos. 

 Tyrone and Derry, and the deposits of pipe clay with lignyte in the 



1 It should be mentioned that on the east of the St. George's Channel, opposite 

 to those in Wiciilow, are found still higher deposits of shelly drift. The Welsh, 

 shelly drifts are, however, separated from those ia, Wicklow by the system of 

 faults that occur in the valley of St. George's Channel, which is probably in the 

 aggregate a great downthrow to the westward, as the drift in the east margin of 

 Ireland seems to rise towards the upthrow of a fault. 



