48 Correspondence — Mr. S. G. Perceval. 



of the Glenthomas valley. The greater part of the specimens I 

 obtained were from its surface, and associated with a small variety 

 of schorl ; it also occurs under similar circumstances on the east side 

 of the ridge above the landslip, on the surface of some smaller slips. 

 Magnetic iron likewise appears on the weathered surface of some 

 neighbouring rocks, of which I procured some fine specimens, and 

 near the west summit of the mountain I found a peculiar form of 

 Andalusite. Few crystals of Titanium are to be obtained, except 

 amongst the debris of the above localities, scarcely any being observ- 

 able amongst the numerous outcrops of the adjoining strata. 



The crystals of Eutile are in colour red or dark metallic brown, 

 frequently geniculated, and occasionally of considerable size. A 

 specimen which I presented to the Museum of the Eoyal Dublin 

 Society was nearly 4 inches in length and in width about ^ inch. 

 I have also given specimens to the Museums of Trinity College, and 

 of the Geological Survey of Ireland. 



Titanium is probably widely disseminated in minute quantities 

 through the mountains north of Clew Bay, though rarely occurring 

 as a distinct mineral. Traces of iron may frequently be observed. 

 and minute crystals of schorl as well as a specimen resembling rutile 

 I noticed near Birreencorragh, but nowhere in the district have I 

 found these minerals in such development as on Cushcamcurragh. 



S. G. Pebceval. 

 Henbdry, N'ov. 25th, 1868. 



SUPPOSED PHOLAS-HOLES ON CONWAY MOUNTAINS. 



SiK,— In a letter, printed on p. 377, Vol. IV., Geol. Mag., Mr. 

 Maw cites the information of a friend who had seen Pholas-borings 

 high up on the mountain to the west of Conway. In answer to an 

 application, the observer has kindly mentioned his locality to me, 

 describing the holes as " of two species, very numerous, the rock 

 being one mass of holes, large and small, .... honeycombed 

 in every direction, like a sponge." The place is a small quarry, on 

 the north side of the very ridge of Conway mountain, and may be 

 best reached by climbing the hill straight up from the Bangor Road, 

 at the west side of a gravel quarry, at the foot of a huge round- 

 headed rock westward of the Railway Bridge there. 



As the observation seems to have been too hasty, I will beg you, 

 in order that it may not lead to misapprehension, to insert this note. 



The so-called Pholas-holes are not the work of any animal. They 

 occur throughout the rock, and not on the surface only. The rock 

 is a vesicular felspathic trap, with many larger or smaller oval cells, 

 most of which are lined with a laminar deposit of crystalline matter. 

 Some portions of it are honeycombed, others full of communicating 

 holes, so as to look not very unlike coarse sponge. The larger holes 

 in exposed places, with thin laminar lining, have weathered, so as 

 to present a considerable likeness to Pholas-holes with shells in, but 

 inspection will at once prove their purely mineralogical character. 



R. D. Daebishire. 

 26, George St., Manchester, \th Bee, 1868. 



