114 
JOURNAL OF THE GEOLOGICAL SOCIETY OF DUBLIN. 
When we descend the mountains from their tops to about 2300 
or 2000 feet, we find many blocks more or less water-worn, and the 
sides and summits of the hills more or less rounded. Hence we 
are enabled to determine the amount of elevation to which this por¬ 
tion of the county of Kerry has been subjected since the period of 
the ice-bearing sea. 
It is remarkable that Mangerton Mountain, though 2756 feet in 
elevation, presents a marked difference in outline to those less ele¬ 
vated peaky summits,—Purple Mountain, Tomies, and Skregmore; 
it is quite rounded on all sides, and flat for a considerable extent 
on its summit. This, however, may be accounted for, by supposing 
a difference in the original form of the mountains and valleys before 
the period of the glacial sea. 
The surface of all the rocks in the Black Valley, as well as on 
the flanks of the adjoining hills, and along the shores, and on the 
islands of the Upper Lake, are all smoothed and striated, in lines 
and small furrows, running east and west, or parallel to the longest 
axis of the valley. All detached rock masses are rounded so as to 
form noses facing the west, a fact which determines the direction 
of the drift in this locality,—though such currents may have been 
merely local. The theory of a great northern drift is not invalidated 
by these observations; because, in the flats along the northern flanks 
of the chain of mountains which extend from Carrantwohill to beyond 
Mallow, boulders of porphyritic and syenitic granite are frequently 
observed, especially on the coal-measures and limestones to the north 
of Mallow. Mr. Du Noyer remarked that in the limestone gravel 
close to Clonmel, county of Tipperary, he had formerly observed a 
rounded lump, from the “ Greensand,” or mulatto stone of the 
county of Antrim, containing its characteristic fossils,—the most 
easily detected of all the cretaceous rocks of the north of Ireland. 
At the period of the last elevation of the Reeks, Carrantwohill, and 
the adjoining mountains, the current set in from the west and south, 
and at the place now called the Gap of Dunloe, a branch current to 
the north ran through it from out of the Black Valley; all along 
this valley the rocks are striated north and south in many places. 
When the lower green grits at the south of the Gap came to be 
acted on, they resisted the wear and tear of the sea, deflecting the 
current to the east so as to leave the head of the Gap dry land; the 
whole force of the water was now applied against the west flank of 
