GEOLOGICA SOCIETY OE DUBLIN. 
59 
sandstones of Slieve Aughta, which lies at no great distance in those 
directions. Neither is there any granite in this cliff, which corroborates 
the evidence of the Barna cliffs, that their materials did not come from 
any northerly source. It is proved, therefore, by the Barna cliffs, that 
this “ clay drift” was not transported from any point of the compass in 
the north segment contained between the west and east. The Aughi- 
nish cliff proves this also, and to that segment adds from the east to the 
south-east; consequently, it must have been carried from some part of 
the smaller segment between the south-east and the west; a conclusion 
that is confirmed by the absence of granite in the drift of Aughinish ; 
but I have found no data that might enable us to define its course 
more exactly. 
The “ great boulder drift” has left ample evidence of its progress. 
The Barna cliffs are strewed over with large granite and limestone 
blocks, and the granites, which are very different from those in the drift 
below, are easily recognisable as belonging to the rocks of the district 
to the north and north-west of Barna. The limestone boulders, which 
are less numerous, probably came from the district west of Lough Corrib; 
and some of them present the arenaceous appearance that I have re¬ 
marked in the limestone about Oughterard near its junction with the 
granite. At Aughinish, though the drift there, as already stated, is un¬ 
mixed with granite, still many boulders of that rock from the north¬ 
west are found on the surface of the land above. They are smaller and 
rounder than those on the Barna cliffs; and they may be traced over the 
country towards Slieve Aughta. 
I think the distinction, direction, and sequence of these drifts are all 
sufficiently proved by the above examples. The distinction and se¬ 
quence, and, less clearly, the direction, are shown where the boulder 
drift overlies detached masses of the clay drift in the granite country 
between Barna and Lough Corrib; as at Tonabrocky Hill, two and a half 
miles north of the Barna cliffs (0. S. 81); and at Glenlough, three- 
fourths of a mile N. E. of Tonabrocky (0. S. 82), where the clay drift 
shows signs of denudation before the deposition of the granitic gravel. 
The direction alone is proved by phenomena observable throughout the 
whole district referred to by this paper, and of which I will give a few 
examples. 
At St. Brandon’s Island, three miles S. E. from Galway (0. S. 94), 
we find large igneous boulders, the parent rocks of which lie to the 
north-west in the vicinity of the town. 
About five miles 8.W. of Oughterard (Galway O.S. 67), on the road 
from the village of Doon to Letter, and at less than a mile from the for¬ 
mer, is a drift hill containing a large block of sandstone, but chiefly 
composed of the debris of hornblendic rocks. Leaving the road a short 
distance farther on, and ascending the hill to the right, the hornblendic 
rock is discovered in situ , covered with great boulders of syenitic por¬ 
phyry, a characteristic rock with large crystals of flesh- coloured felspar 
and green hornblende; and this also may be found in situ at Knockalee 
Hill, at a distance of near two miles in a direction rather north of west. 
