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 Bally edmonduff, 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 Killiney 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, have been gradually drifted along the coast by the 

 ordinary action of the waves. 



