of the North of Ireland, 235 



which In both amounts nearly to the angle of the dip of the outward 

 surface of the hill which they compose." 



" These differences seem to have resulted from the greater vicinity 

 of the cliffs at Somma to the seat of the crater as well as to the 

 more rapid slope of the hill, which from the greater degree of 

 fluidity of the lavas, and their more rapid tendency to descend, did 

 not allow them to acquire there any considerable thickness ; whereas 

 in Antrim the distance being probably greater from the crater, and 

 the slope much less, the lavas could settle there in greater depth. 

 The basaltic walls also found along the coast of Antrim, and parti- 

 cularly of Ballycastle and Belfast, seem to have a perfect analogy 

 with those of Somma, but are of much greater breadth in general, 

 and the intervening strata of porous and irregular basaltic matter 

 between them correspond exactly with those of scovix in all lavas, 

 and so visible in the ancient ones of Somma." 



" In the side of one of these walls of Somma, I found a crust of 

 completely vitrified matter, covering a schistose cracked and very 

 fragile homogeneous lava, disposed, contrary to the general rule of 

 that kind, in perpendicular joints, and much resembling a kind of 

 schistose hornstone, as well as the upper and superficial covering of 

 Pleaskin." 



" The whole of the valley between Somma and Vesuvius is 

 covered with repeated irruptions of lava, particularly those of 1 767, 

 1779, and 1787, which have run to the foot of the rock and 

 to a considerable depth." 



This description will be found to agree pretty well with that of 

 M. Breislack (Voyages dans la Campanie. tom. 1. p. 13.3. Paris 

 1801.) ; from both of which It is sufficiently clear, that the walls of 

 Monte Somma are of the same nature with the dykes of the north 

 of Ireland. 



2 G 2 



