108 On the basaltic Surface of the Counties 



to the summit, vanishes with it (at x in the view of Port" 

 mnon), and is seen no more* 



These ochreous matters, so common in all basaltic coun- 

 tries, according to Mr. F. St. Fond's opinion, were once 

 pure basalt, but have undergone some chemical process of 

 nature we are unacquainted with, by which their colour has 

 been changed. 



Third Stratum , (i). 



The next stratum is the last of those composing the pro- 

 montory which appears beyond it; for so long as the first 

 and second continue their horizontal course towards Bevgore, 

 this third accompanies them, showing its upper surface be- 

 tween high and low water- mark ; but when it ascends along 

 with the others across the facades ir displays its whole 

 thickness, above fifty feet. 



This stratum is of that variety of basalt, I have on diffe- 

 rent occasions distinguished by the name irregular prismatic ; 

 it resembles the columnar basalt in grain, but differs from 

 it totally in principle of internal construction, for its prisms 

 are small, not articulated, and indifferent as to the position 

 of their axes, which is perpetually changing. 



The irregular prismatic basalt accompanies the columnar 

 in most countries, as at Pont dti Baume, at Trezza, at Bol- 

 sena in the Sound of Mull, and at Staffa. In Antrim, it is 

 very common ; and here is a striking resemblance between 

 the rock crowning the celebrated columns at Staffa, and a 

 stratum covering a very neat colonnade at Crai galiullur , near 

 Portrush. 



This stratum (as is well exhibited in the view of Port- 

 moon) is scolloped off irregularly from the point where it be- 

 comes superficial (x), until it completely disappears at (?■)> 

 a thin stripe of its lower edge alone is ever resumed again. 



Fourth Stratum, (h). 

 The next three strata will require only very short descrip- 

 tions; the fourth is about seven feet thick, entirely colum- 

 nar, the pillars small, but not neat : they appear very white 

 from a thick covering of Byssus saxatilis, which shows a 

 great predilection for this sl'a'uro. 



Fifth 



