250 



THE GEOLOGIST. 



(PI. XIII.), and there is a superstition tbat on All-Hallow Eve tbis 

 mass floats off into the lake, returning to its present resting-place ere 

 cockcrow. This remarkable block consists of a seriesof purple grits, and 

 thin purple earthy layers, and now measured roughly is 40 x 25 x 16 

 feet, representing a bulk of about 16,000 cubic feet, and weighing 

 about 1100 to 1200 tons. Originally this mass was much larger, 

 as large flakes have fallen ofi" its sides from the result of atmospheric 

 action. 



On the Carboniferous slate district to the S.W. of Dunmanway, at 

 the summit, marked 964 feet to the west of Millane Hill, there is a 

 perched boulder of hard light grey gritty slate, measuring 6 x 4|- x 2^ 

 feet, which is known to the peasantry by the name of" Gallaun Keogh." 

 To the north of Dunmanway in the Townland of Gurtanure, and at 

 the junction of the Caha with the Bandon Hiver, a rocky boss afl'ords 

 some very interesting examples of "roches moutonnees " and glacial 

 striae. Here we find purple grits weathering into small pinnacles on 

 the lines of the dip, the cleavage and the cross joints, the sides and 

 angles of which are rounded and polished and marked with well- 

 defined horizontal striae. On the level polished surfaces of rock, we 

 find the same peculiarity of form in the scratches as before noticed. 

 They are fine at the end pointing to the N.N.W., and blunt at that 

 pointing to the S.S.E., thus clearly indicating the direction from 

 which the current came which floated the ice-masses forming them. 

 The horizontal markings have not however this peculiarity, but are a 

 series of fine groovings and sharp scratches. 



Over the Carboniferous slate to the south of Dunmanway the 

 compass bearing of the glacial striae is generally the same as that 

 over the Old Eed Sandstone, and the mountainous district to the 

 north. This is very well seen in the horizontal and smooth rock 

 surfaces to the north of Ballinacarriga Lough, at an elevation of 339 

 feet, where the striae run N. 20 W. and S. 20 E., the thin end of the 

 scratches being presented to the former point. 



The accompanying illustration of a perched boulder from near 

 Dunmanway (PL XIV.) is interesting in many respects ; it shows 

 how readily the sandstone yielded on the planes of the slaty cleavage 

 to wliat must have been the sudden concussion of an iceberg ground- 

 ing on sucli a submerged inequality in the sea bottom as this rocky 

 boss must have been. The view is taken looking somewhat to the 

 westward. The general form of the rock when it was submerged in 

 tlic glacial sea must have been very nearly the same as now, one side 



