On the Physical Geology of the Neighbourhood of Dublin. 155 
hood all belong to species now inhabiting the neighbouring seas ; 
they are usually much broken, especially those found at the 
higher elevations. ‘The highest. places at which they have been 
found are at Ballyedmonduff, 1,000 feet, and.at one furlong south- 
ward of Caldbeck Castle, on the above mentioned col between the 
Three Rock and Kilmashogue Mountains, 1,250 feet above the sea. 
It is most probable that a large proportion of these deposits 
consists of water-rolled and rearranged materials derived from 
the Boulder Clay which seems to have suffered denudation and to 
have been removed in some of those places, at least, where the 
water-formed gravels lie directly on the rock. The gravels have 
been piled very irregularly ; some valleys contain deep accumu- 
lations of it. Some places are bare of it, though situated at lower 
levels than others not far off which are deeply covered. 
There are great collections of this formation in Killakee valley, 
in Glennasmole (shells), in many places in the valley of the Dargle 
river from Bray towards Powerscourt) Deer Park, in Glencullen, 
about Enniskerry, &c. There are fine natural sections in many 
places, especially Kalliney Bay (shells) and Balscaddan Bay on the 
E. side of Howth Harbour (shells), and many good artificial 
sections in large gravel pits about the neighbourhood. 
It is just possible that these gravels may have formerly 
reached higher elevations than those mentioned and have been 
washed down again. On the Two Rock Mountain, which might 
be called the southern and higher part of the Three Rock ditto, 
stones of two to four inches in diameter, and blocks of extrane- 
ous material can be found near the summit at 1,750 feet. There 
are two blocks of granite on the N.W. side of the Great 
Sugar ‘Loaf, at the height of 1,480 feet, and several others at 
1,300 feet; these are three miles from the nearest granite rock ; 
there are some also on the upper part of Bray Head, five miles 
from the nearest granite. These may have been transported by 
floating ice, which agent has, doubtless, dropped the large blocks 
of (local) granite which may be seen resting on the surface of 
the above-mentioned elevated gravels of extraneous materials 
resting on the granite hills. The numerous fragments of chalk- 
- flint and the pieces of Mourne granite that are found in the 
gravels may have been carried hither by floating ice; they may, 
however, bave been gradually drifted along the coast by the 
ordinary action of the waves, 
