CiiAELESWORTH — Glacial Geology of North- West of Ireland. 1 95 



stratified gravel, are seen to overlie a boss of water-worn schistose rock. 

 The red sand and gravel deposit is overlain by 25 to 30 feet of the usual 

 yellowish boulder-clay of the country [the Donegal boulder-clay]. This 

 gravel deposit is evidently connected with the early or Scottish ice-sheet, 

 for the stones in it [chalk-flints, chalk, triassic, and carboniferous 

 sandstones, tertiary dolerites, schists, and local rocks] are such as would 

 be derived from the washing of the older boulder-clay deposits." 



It will be noticed there is no true Scottish boulder-clay, and the question 

 naturally suggests itself, whether these sands and gravels of the lower part 

 of the section may not represent the water- worn sands and gravels formed as 

 outwash sheets along the front of the Scottish ice. Signifieantly, the location 

 of the deposit is just on the line where, from the other data already presented, 

 the edge of the ice is presumed to have stood. This would indicate that a 

 tract of ice-free country, of unknown extern;, lay to the south, where the 

 outwash gravels from the ice-face could be spread, and so furnish evidence to 

 the effect that the Scottish and the Donegal ice-sheets were at any rate at 

 this period discontinuous. The very large pre-glacial valley, now virtually 

 sti'eamless and floored with drift, which runs from Carrigans on the Foyle to 

 the Swilly, may have been the course of the diverted waters of the Foyle, 

 swollen by the melt waters of the ice at Omagh and in Donegal. Ice 

 advancing along the north Antrim coast would doubtless thrust a lobe into 

 the Foyle estuary, probably as far as the site of Londonderry, where the hills 

 come together, long before it covered the adjacent bounding hills of 

 Inishowen and the Antrim plateau. At this stage some of the shelly 

 boulder-clay south of the Foyle estuary may have been laid down, the sands 

 and gravels of the liOw Moor Road section swept out of the ice as outwash 

 gravels, and the flood waters of the Foyle diverted by the valley containing 

 Port Lough into the Swilly. The Donegal ice at this stage would be well to 

 the west. Probably the Donegal and Scottish ice-masses waxed simul- 

 taneously, the invading somewhat faster than the local ice. 



The import of the river sections near Draperstown, however, would seem 

 to be that in this area resistance was offered to the Scottish by the local ice. 

 In a few places in the banks of the "White Water, south-west of Draperstown, 

 extremely fine sections of boulder-clay are exposed. This is seen to rest 

 on rock, and consists throughout from bottom to top of a homogeneous clay, 

 charged with boulders from western sources; No erratics indicative of an 

 eastern source were discovered by Dr. A. R. Dwerryhouse or myself. These 

 sections are less than 300 feet above sea-level. 



The overriding of much of Inishowen by Scottish ice seems quite 



