GEOLOGICAL SOCIETY OF DUBLIN. 115 



and the geologist may look in vain there, as well as in Abbey Bay or 

 Bundoran Bay, for a bed or a ball of clay-ironstone. 



The third member of the succession, the gray and reddish-gray sand- 

 stone at Bundoran (which to my eye seems yellow), is not Calp Sand- 

 stone, but Old Bed Sandstone, which, according to the views I entertain, 

 lies under the Carboniferous Limestone of Donegal Bay, and is thrown 

 up here by a fault. Prom Bundoran it continues along the shore by 

 Mullaghmore to the base of Benbulben, near Sligo, a limestone moun- 

 tain with precipitous escarpments and level beds. The fossiliferous shale 

 and limestone in Abbey Bay, close to Ballyshannon and Bundoran, is 

 the Carboniferous Slate, and the limestone at Ballyshannon the ordinary 

 Carboniferous Limestone, being on a low level here, as compared to what 

 it stands in at Dartree and Benbulben mountains, the cause of which I 

 shall presently explain. 



Leaving Bundoran again, and travelling southward, there is no doubt 

 at all of the succession. The Old Eed Sandstone of that place is covered 

 by Carboniferous Slate, having the same dip and strike. Some of this 

 slate or shale is fine-grained, some coarse-grained, all fossiliferous and 

 interstratified with beds of dark-coloured, impure limestone, which in 

 this district increase in number and thickness in ascending, until they 

 are covered by the gray limestone of Dartree mountain, which crowns 

 the precipice, without any apparent interruption of the succession. 



Third objection. — The sandstone at Mullaghmore, west of Bundo- 

 ran, on the sea- shore, is 209 feet above low water, and dips and accu- 

 mulates southward, till it forms a band four miles wide, and several 

 hundred feet in thickness. The Calp, which is stated at quotation 

 "No. 5 to be 1700 feet thick at Bundoran, including these several 

 hundred feet in thickness of sandstone, is at Drumah#ire, twelve miles 

 to the south, diminished, as may be seen on the Map, to a band of in- 

 significant thickness, without any sandstone at all; thus forming a 

 wedge-shaped mass twelve miles long, 1700 feet thick at the north end, 

 and, say, thirty or twenty feet at the south. Can it be believed that such 

 a wedge as this exists in the Carboniferous formation — one of the most 

 remarkable for the persistence and parallel arrangement of its groups — 

 One in which a bed of coal, or a bed of fireclay, two or three feet thick, 

 has often been identified through a district for ten, twenty, or thirty 

 miles ? 



Fourth objection. — Since the limestone at Ballyshannon, and the 

 sandstone at Bundoran, may be matter of dispute, let us leave this de- 

 bateable ground, and take the millstone grit. The base of this rock is as 

 easily determined, and as certain as any boundary line between different 

 rocks in geology. I may say it is particularly so in the west of Ireland, 

 because the rocks are well exposed in precipices and high hills, and at 

 this base form a junction of black shale and gray limestone — two rocks 

 so entirely different in colour and mineral character as to be in no way 

 likely to be mistaken for one another, or the line between them for any 

 other line. 



At par. 13 it is stated that "the shale district, extending from Drum- 



