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.PROCEEDINGS OP THE GEOLOGICAL SOCIETY. 



[Feb. 20, 



ferent from that which they generally assume. They have a pink 

 colour, are much broken up, are devoid of regular arrangement, and 

 exhibit features nearly akin to hornstone. At Sandy Port, traps are 

 seen ; but these have not produced the results above alluded to, and 

 such results do not accompany the other outbursts of trap, which are 

 so abundant along this coast. 



These changes in the quartz-rocks have originated from plutonic 

 masses ; and although rocks of this character are not seen imme- 

 diately on the north-east coast of Donegal, yet at a short distance 

 inland such rocks occur. 



The rock which has produced the hornstone aspect in the quartz- 

 rocks, and given rise to this well-marked axis, is a red syenite, very 

 manifest on the west side of Malin Head ; and this red syenite 

 occupies a considerable area in the north-west of the county of 

 Donegal. 



From this axis at Sandy Port the quartz-rocks continue north- 

 westward to BaUyhillin, where they are succeeded by the overly- 

 ing gneissose series. 



On the north side of this axis the higher members, which south- 

 ward consist of chloritic schist, are represented by a flaggy gneiss, 

 which is well seen in the precipitous rocks on the north-east side 

 of Malin Head ; and lithologically this gneiss is very much allied to 

 the- upper gneiss of Sutherland. Traps are very abundant among the 

 rocks which form the north-east extremity of Malin Head ; and thick 

 veins of white quartz are also prevalent in this locality. 



With reference to the West of Ireland, where rocks consisting of 

 gneiss, limestone, and quartz-rocks are shown to occur, I have not 

 had an opportunity of comparing these as they are exhibited in the 

 County of Mayo with the North of Ireland and with the Highland 

 rocks. But, inferring from the strike and the arrangement of these 

 rocks as they are laid down on the geological map of Ireland, I feel 

 little doubt that they are referable to the same position and sequence 

 as the rocks of a similar nature in the North of Ireland and in the 

 Highlands of Scotland, and that the true position of these rocks is that 

 assigned to them by Sir Roderick Murchison in his " Hypothetical 

 View respecting the Gneissose Bocks of the Southern Highlands " 

 (Quart. Joimi. Geol. Soc, vol. xvi. page 238). 



P.S. [April 6th.] — Since the above memoir was read, the author has 

 again visited the limestone which is worked at Leny, near Callender, 

 for the purpose of endeavouring to procure fossils from the associated 

 black shales. After a careful and diligent search, no specimens could 

 be detected, although the limestone is now being wrought to a con- 

 siderable extent. The face at present exposed shows a greater 

 extent of rock than that above referred to, — no less than twelve feet of 

 limestone with thin black shales being visible, and having well-de- 

 veloped black shales both above and below. A dyke of porphyritic 

 felstone, which cuts the limestone very obliquely to the west of the 

 quarry, is also seen on the north side of the limestone. 



