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VI.— ON THE OCCUEEENCE OF AN OUTLYING MASS OF SUP- 

 POSED LOWEE OLD EED SANDSTONE AND CONGLO- 

 MEEATE IN THE PEOMONTOEY OF FANAD, COUNTY 

 DONEGAL. By EDWAED HULL, L.L.D., F.E. S., Director 

 of the Geological Survey of Ireland. 



[Read, December 16, 1885.] 



The district where this mass occurs lies between Lough S willy and 

 Mulroy Bay, and is formed chiefly of metamorphic beds of quartz- 

 ite, schist, trap, and crystalline limestone. The tract of Lower Old 

 Eed Sandstone lies along the northern base of the Glenalla Hills, 

 rising into a high ridge of quartzite, &c, which strikes across the 

 promontory in a N.E. and S.W. direction, and attains to an eleva- 

 tion of 1,196 feet. The beds of sandstone and conglomerate are 

 let down by a large fault against the older rocks, and form a low, 

 rocky tract, lying for about two miles along the northern base of 

 the mountain, and were recognized by the officers of the Geological 

 Survey when engaged in that district during the summer of this 

 year. They consist of alternating beds of reddish soft sandstone, 

 generally pebbly, and often forming massive conglomerates, with 

 large blocks of quartzite, schist, limestone, and trap. 



The dip of the beds is S.S.E., or towards the base of the quartz- 

 ite ridge ; and, measured across the strike, the mass is one-quarter 

 of a mile across, and the estimated thickness is about 800 feet. 

 Eed shales, and flaggy sandstones also occur, and are seen resting 

 unconformably on the quartzite beds of the metamorphic series. 



From the general resemblance of these beds to those referable 

 to the age of the Lower Old Eed Sandstone in the district of 

 Omagh and Dromore to the south, as also on the coast of Antrim 

 and Scotland in an easterly direction, I am disposed to refer them 

 to this formation, rather than to one of a more recent period, such 

 as the Carboniferous ; but in the absence of fossils and the entirely 

 isolated position of the beds, the question of their geological age 

 must remain somewhat indeterminate. They seem to have been 

 formed within the limits of a basin separated from any of the other 

 basins of Lower Old Eed Sandstone either in Ireland or Scotland, 

 and will prove a new feature in the Geological Map of Ireland. 



