166 Archdeacon Verschoyle on the Geology of the North Coast of 



Dromahair, in the county Leitrim, running parallel to the river, which falls into the east end of 

 Lough Gill ; and here an unusual change occurs, the material of the vein consisting of vertical 

 layers of serpentine. The mica slate, when in contact with the vein, presents a bright red colour, 

 and crumbles between the fingers, as if it had been intensely heated ; and veins of asbestos occur 

 abundantly in the dyke between the coarse laminae which compose it. The schist rises towards 

 the vein at each side, as if it had been elevated by a force from below, and the serpentine forms 

 a narrow line of hill along the river, where its stream turns to the eastward, opposite Friarstown, 

 about half a mile from the town. I have not traced it further, but there is no appearance of a 

 termination. 



No. 4. This dyke is found in the west side of Erris Head, where a pigeon hole (as those caverns 

 in the cliffs, with an opening in the roof are called) has resulted from its disintegration. It 

 appears again at the opposite side, rising from the water's edge to the summit of the precipice ; 

 and it crosses Broad Haven, but the drifting sands at the mouth of the Glanamoy River conceal 

 its course, as do the bog and moor to the valley of Ballinglan. At the last locality, the shale 

 and grit beds are much deranged by its influence, the shale being indurated and converted into 

 a black quartzy chert, rifted most irregularly, and the crevices are filled with quartz, highly 

 crystalline, and shooting into hexagonal pyramids ; and the layers of grit are disturbed and fis- 

 sured. It is prolonged thence to Kilcummin, appearing in the road on the west side ; and traver- 

 sing the head it is seen among the rocks on the sea shore, near Castlemagee. It is there por- 

 phyritic, being chiefly composed of large tabular concretions of felspar, and contains augit and 

 green earth. On the east shore of Killalla Bay, it passes through the limestone, and may be ob- 

 served further east, at Conquil Bridge, and is well displayed at Dromore West, having there raised 

 up the limestone at each side, altered the colour, and rendered the structure more granular. It 

 constitutes the fall in the river close to the bridge ; beyond which the stream runs in a deep 

 ravine, caused by the decomposition of the limestone, but the dyke lines one side of the bank 

 some distance below. It has been observed by Mr. J. Wynne, of Hazlewood, at Dromiskeybole, 

 near the west end of Lough Gill ; and in the pass through Slish Mountain, close to the Ballintogher 

 road, it either sends a branch to the north-west, or is crossed by another dyke. I have, as yet, 

 been unable to determine this point, but a ridge of serpentine is found there, near and parallel to 

 the road, for the repair of which it furnishes the material. There is almost an identity between 

 specimens from this site and those from the Dromahair dyke ; they are both laminated, both con- 

 tain asbestos, and agree in colour and hardness. My examination terminated here. 



No. 5. This dyke first appears as a singular and picturesque narrow stair-case of prisms, ascend- 

 ing from the sea between two high walls of indurated mica slate, almost porcelainised by its contact, 

 and the schistose structure is obliterated. The steps consist of short columns, lying horizontally 

 across the vein, from side to side. Penetrating the peninsula of Erris, and crossing, eastward of 

 Broad Haven, the district of Kilcommon, the peat and soil conceal its course, till it appears in 

 Ballinglan, where it can be traced up a ravine through which a stream flows from the moory summit 

 of Knock Aghleeg ; and on the east side of that hill, it crosses the stream of Carrickanass, traversing 

 the beds of sandstone without any apparent effect. It continues thence by Rafron and Ross to the 

 Bay of Killalla, passing for some distance through the bed of trachyte, where it assumes the 

 appearance of basalt, black, fine-grained and prismatic, in one place regularly columnar, and the 

 pillars are as neatly defined as those of the Giants' Causeway, but their axes are nearly horizontal, 

 being at right angles to the walls of the vein. In Palmerstown River it appears like three walls 

 of polygonal prisms, built in contact with each other ; and the surrounding rock having been de- 

 composed and washed away, its construction is laid open. The prisms where weathered, peel off 



