235 



XXX. — On the Geology of the County of Antrim, with Parts of 

 the adjacent Counties. By John Kelly, C. E m Fellow of the 

 Eoyal Geological Society. 



[Read May 11 and 25, 1868.] 



GEOGRAPHY AND OROGRAPHY OF DISTRICT. 



The county of Antrim is bounded on the north by the Atlantic Ocean, 

 on the east by the Irish Sea, on the south by the counties of Down 

 and Armagh, and on the west by Derry and Tyrone. It is 54 miles 

 long from Bangor Head, on the north, to the Aqueduct bridge, near 

 Moira, on the south ; and 34 miles in its greatest breadth, from Black 

 Head, near Carrickfergus, to Toome Bridge. It contains, by the Ord- 

 nance Map, about 1190 square miles. 



This county, and the eastern part of Derry, are so nearly similar in 

 mountains, in rocks, and in fossils, that for the physical features, the 

 geology, and the palaeontology, they may be joined together, and 

 treated as one. General Portlock has, however, written on Derry, and 

 parts of Tyrone. I do not mean to go into details after him, except 

 by an occasional reference where there may be suitable matter to illus- 

 trate the adjacent parts of the country. In the map, therefore, accom- 

 panying this paper, I omit the whole of the county west of the Baim 

 River and Lough Neagh. 



This area, taken as one, is composed of two high ridges of land, 

 one on the east, and one on the west side of the district : both assum- 

 ing a north and south direction, and with a wide depression between them, 

 which runs in the same direction, in which lies the valley of the Bann 

 River and Lough Neagh. This depression may be taken to be at the 

 level of the sea ; for the Bann, at Coleraine on the north, and Carling- 

 ford Bay on the south, are at the sea-level ; while the bottom of Lough 

 Neagh, about midway between them, may also be considered to be so ; 

 for though the surface of the Lough is 48 feet above the sea, its depth 

 is as much, or a little more ; so that at those three points the surface of 

 the rock is on the same level, and the intervals between them, I 

 may say the bottom of the depression the whole way, not much 

 different. 



Taking the Antrim side in itself, it forms an inclined surface, high 

 on the east side, near the coast, and low on the west, along the afore- 

 said valley. 



It is a matter of some interest to compare the heights of the two 

 ridges on the Antrim and Derry side. For this purpose I have drawn 

 up the following Table from the Ordnance Survey, showing the heights 

 along the crests of both ridges : — 



