Chaijlesworth — Glacial Geology of North- West of Ireland. 19J 



The whole of Inishowen, therefore, with the probable exceptions of its 

 higher parts, e.g. Slieve Snaght and Eaghtin More, would appear to have been 

 overridden at this stage by the Scottish or eastern ice. In the north the ice 

 passed in a general westerly direction along the great depression, extending 

 from Culdaff to Lough Svvilly ; the striae and grooves running slightly south 

 of west, observed at Fegart at the eastern extremity of Doagh Island, may 

 have been produced at this time. 



Further south, this ice-sheet would tend to bear in a more southerly 

 direction, and overriding the northern foot hills of the Sperrin Mountains, 

 impinge on the slopes of these mountains in a direction almost at right angles 

 to their course. 



The entire absence of any trace of Antrim or eastern erratics in the 

 Donegal drift west of the Swilly suggests, in view of their abundance on the 

 Inishowen side of that inlet, that the highlands of Donegal were never 

 invaded by the Scottish ice, but that its western limit was roughly coincident 

 with the line of IjOugTi Swilly. 



As already pointed out, J. R. Kilroe postulated a glaciation from the 

 north, intermediate between the Scottish and later local glaciations ; the 

 shelly drift just described, more particularly, however, that occurring some 

 12 miles inland at 500 feet O.D. in the bank of a stream bounding Gortnarne, 

 is part' of the evidence upon which he bases this additional glaciation. He 

 writes* : — 



" The ice-sheet bearing these materials must have flowed southward 

 with a fair measure of directness, else it could scarcely have borne- the 

 materials to such a height on the east side of the valley [Eoe.] On the 

 sea-floor it would have found shells, mingled with marly clay and 

 rounded dibris of the basalt, as well as splinters of chalk and chalk- 

 flints, many of which stud the Boulder-clay." 



It is, however, scarcely necessary to have recourse to a separate glaciation to 

 explain these shelly boulder-clay occurrences. They are but part of the 

 basalt and flint-bearing drift whose distribution in this northern area has just 

 been traced, and are therefore to be conceived, equally with this, as the pro- 

 duct in this area of the Scottish ice of the north-east of Ireland and not of a 

 glaciation distinct from this in area and in date.^ 



1 The remaining part will be dealt with in a later section. 



2 Proc. Belfast Nat. Field Club (1913), p. 651. 



= We may, perhaps, quote Mr. Kilroe against himself. In the ' ' Londonderry Memoir " 

 (p. 56), referring to these shell-bearing deposits in the Roe Valley, he says :— These are 

 "suggestive of an ice-movement across the County of Antrim, which would be in accord 

 with the east-to-west striae above mentioned. There is no record of striation along the 

 Bob Valley indicative of an ioe-fiow towards the south." 



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