126 The Rev. W. Conybeare on the 



describing that system, it is necessary to observe that another small 

 coai field occurs at Ballycastle, near the edge of the mica slate 

 district in the north-east of Antrim. 



there are points of agreement and points of difference : the great features of agreement are 

 those mentioned in tlie text, namely, that both occur in the vicinity of coal fields, and iu 

 a position intermediate between the northern and southern mountain chains. The points 

 of difference are, that the Campsie hills seem, at least along their southern border, to 

 repose immediately on the coal measures ; and the same observation may be applied to 

 the junction of the Ochills with the coal field of Clackmananshire at Westertoun. 

 Whereas the basalt of Ireland is generally separated from the coal measures by several 

 intervening beds of considerable importance and of much more recent formation, which 

 appear to be altogether wanting in Scotland, It may be even objected to the instance 

 of Cross hill near Fairhead, which is cited towards the end of this introduction as aa 

 example of the occurrence of trap in Antrim under the same conditions with that of 

 Scotland, namely, in contact with the coal measures, that the trap in this instance and 

 through tlie whole range of Fairhead, assumes a character so widely different from the 

 compact and small grained basalt of the neighbourhood, (being a highly crystalline green- 

 stone) as almost to warrant the suspicion of its being a distinct formation, notwithstand- 

 ing its close geographical proximity to the great basaltic mass. I confess myself however 

 to be fully persuaded that this suspicion will on further examination be found groundless. 

 The rock in question closely agrees in its texture with that of Slievemish, which it is quite 

 impossible to detach from the general mass of trap. The island of Arran appears to form 

 an important link in the connection I have endeavoured to trace, between the opposite 

 coasts of Ireland and Scotland ; the center of this island is occupied by a primitive district, 

 comprising granite, mica slate and syenite ; the mica slate extends to and skirts the N.W. 

 coast. The N.E. coast presents a small coal formation precisely analogous to that of Bally- 

 castle, with beds of breccia and of red sandstone resembling those which occur in the Antrim 

 coast near Newtown Glens ; this sandstone forms the prevailing substratum through the 

 whole south of the island, where it is covered by a singular columnar clay porphyry, and 

 by greenstone, both of which rocks are generally referred to the floetz trap series. It 

 seems probable that the porphyry which occurs on the opposite coast of Cantire at Devar 

 near Campbelltown, and the syenitic rock which forms the crag of Ailsa may be considered 

 as connected with these formations. The whole island is traversed by numerous dykes of 

 basalt and pitchstone. A similar structure is continued through the corresponding portions 

 of Bute. And an exact resemblance prevails between the northern and southern districts 

 of these islands and the opposite coasts of the estuary of the Clyde in which they are 

 situated ; thus the primitive rocks, forming the north of those islands, are resumed on the 

 north of the estuary in Cowal and Cantire ; while the sandstone, breccia, and trap rocks of 

 their southern district are continued in that direction through the Cumbray isles, and at 

 Largs and the whole southern bank of the Clyde : the line of junction between these 



