100 REPORT — 1871. 



fronisontli to north, crossing- the Curlew and Ox mountains in the county of Sligo, 

 the direction of each being from north-east to south-west. 



The Curlew mountains consist of brown sandstone belonging to the Upper Silurian 

 series, the surface being elevated above 800 feet above the level of the sea. 

 Descending the mountains to the north, to the limestone vaUey of Tobercurry, 

 which occurs between them and the Ox mountains, we find the surface with very 

 large boulders of brown sandstone ; and continuing to tlie northward the ascent of 

 the Ox mountains, which are composed of mica-slate, we find the boulders of 

 brown sandstone continued, though diminished in size. On reaching tlie height 

 of 450 feet above the limestone valley, we meet with limestone Eskers having an 

 east and west direction, crossing the mountain valley at right angles, and on top 

 of which numerous angular blocks of mica-slate rest ; but the mica-slate is inter- 

 mixed with gravel, which is composed altogether of clean rolled masses of Carbo- 

 niferous limestone. Milan Mountain, one of the Ox range, the summit of which is 

 elevated to the height of 1446 feet above the sea, is composed of granite, forming 

 part of a large protrusion through the mica-slate, which is metamorphosed near 

 the contact. 



This gi-anite is large-grained, and is composed of red and white felspar, grey 

 quartz, and black mica, but without any crystals of red felspar such as occur in 

 the Galway granite. 



Descending the mountains to the north, we reach the Easky Lough, elevated 

 700 feet above the sea. Here the granite is bounded by mica-slate, which continues 

 to the base of the declivity, and we find the surface covered by blocks of granite ; 

 and continuing still further across the limestone plain to the sea-coast, to Easky 

 village, a distance of 8 miles, we find the surface also covered by very large blocks 

 of granite ; and one in particular, which is situated within half a mile of the sea- 

 shore, and near to Easky village, was, on measurement, found to contain 13G0 

 cubic feet, equal to 100 tons in weight. 



Similar granite blocks occur on the surface of the whole line of the north coast 

 of Sligo and Mayo, all of which are similar in composition to the Easky granite, as 

 well as to that which occurs on the summit of the Ox mountains to the west of 

 Easlcy Lough as far as the town of Foxford ; and no doubt can be entertained that 

 such must have been transported by ice. 



On the Ar/ency of the Alternate Elevation and Subsidence of tlie Land in the 

 formation of Boidder-clai/s and Glaciers, and the Excavation of Vallei/s 

 and Bays. By the Eev. Johx Gunx. 



Mr. Gunn briefly recapitulated the contents of a paper which he read at the 

 Meeting of the British Association at Liverpool, to the eifect that boulder-clays 

 were deposited in a temperate rather than in a glacial period, inasmuch as the 

 area of the sea was increased by the subsidence of the land ; the perpetual snow- 

 line must have been lowered, masses of ice disengaged, icebergs set floating and 

 the boulder-clays formed ; that the glacial epoch was due to the elevation of 

 mountain-ranges and consequent glaciers. He proceeded to show that, in some 

 instances which he specified, the agency of the alternate elevation and depression 

 of the land in scooping out valleys and gorges where there was no evidence of ice 

 action might be traced ; that such effects were due to the action of shallow seas, 

 either while clearing oil', or while gathering over the surface of the land, and cutting 

 out with its incessant surge water-worn channels and inland bays. He stated, in 

 conclusion, his opinion that there was no occasion to invoke any additional causes 

 of change of climatiire besides those which were kno^vn to exist ; but the question 

 which remains to be soh'ed is, to what cause are these alternate oscillations of 

 level due ? 



Professor H.^rkness, F.R.S., F.G.S., exhibited one of the earliest forms of Tri- 

 lobites. 



