468 



5ade extends a full mile, I have been able to difcover but one dyke, 

 and in the mighty face of Magiliigan Rock not one. 



Dr. HutWi admits, (page 259), that, in deep ftrata, the veins 

 are wide, in thin ftrata narrow ; but in the faces of our precipices, 

 where fome ftrata are many times as thick as others, yet the fiffures 

 (filled, as he fuppofes, by our whyn dykes) are of uniform breadth in 

 every ftratum they cut. 



He tells us alfo, that contiguous Jlrata fuffsr unequal degrees of con- 

 irailion ; no doubt, for, fitting in his ftudy, he could never conceive 

 that ftrata of freeftone and of bafalt would fuffer the fame contraftion with 

 thin veins of coal, knowing that different fubftnnces have different degrees 

 of contraftability ; but each whyn dyke, cutting tliefe ftrata, at the colliery 

 near Fairhcad, preferves an uniform breadth from top to bottom ; the more 

 accurate perpendicularity of the lofty precipices about the Giant's C'aufe- 

 way, exhibits this circumftance to great advantage in the dykes at Ro- 

 vinvalley and Port Spagna on its eaft, and at the Mile Stone on its 

 weft fide ; in thefe places the uniform breadth of the dyke is ftrongly 

 contrafted with the different thickneffes of the ftrata. 



When difcufling Dr. Hutton's pofiiion, that our ftrata were formed 

 by depofition at the bottom of the fea, I fliewed how incompatible 

 that opinion was with the ftate in which thefe ftrata are aftually 

 found, that is, accumulated upon each other in great numbers, of dif- 

 ferent materials, and each ftratum compleatly diilincl from the con- 

 tiguous one?. 



The difficulty feems equally unfurmountable, when he comes to con- 

 folidate thefe diftinft ftrata by igneous fufion, according to the tenor 

 of his fecond propofition ; for he muft take his choice, either to kin- 

 dle a fire at the bottom of the fea, fufe and confolidate each ftratum 

 feparately, as foon as formed, then put his fire out, and wait until 

 another ftratum be ready for him, and fo on ; or he muft fufe the 

 whole mafs at once, without fuiFering the heterogeneous materials to 



mix. 



