PREFACE. XV 



spar, with imbedded crystals of the same. When these rocks 

 occur in the manner, and with the characters now described, 

 it is usual to consider them as subordinate to the old red 

 sandstone ; but where no formation of this kind is observable, 

 and where the rocks within a few yards are evidently grey- 

 wacke, as they are in the situation now before us, there seems 

 no other way of describing the trap rocks of St Abb's but as 

 subordinate to the transition greywacke and greywacke-slate. 

 We have described St Abb's as an insulated mountain mass, it 

 being completely cut off from the wide extent of high ground 

 towards the west by a deep valley, in the centre of which is a 

 marsh of considerable botanical interest. 



" There are probably few places where the contrast, both in 

 external aspect and in botanical phenomena, as well as in 

 structure, is so remarkable, as it is between the two sides of 

 this valley, especially at the little inlet termed Petty cur wick. 

 Standing by the sea-side at this small creek, and looking west- 

 ward, we perceive, for many miles along the lofty coast, the 

 most splendid displays of stratification, the strata being of all 

 forms, and in all positions, curved, zigzag, vertical, horizontal, 

 &c. ; but the outline both of the summits and the slope of the 

 precipices, we observe, in general, to be smooth and unbroken, 

 and more like a vast sloping wall or mural defence, than a na- 

 tural piece of rock-scenery. Looking towards the east again, 

 which consists of the high ground of St Abb's, the outline is 

 rugged, broken, and highly picturesque, the sea in that direc- 

 tion being ranged with beetling crags and overhanging cliffs, 

 in one place hollowed out into magnificent caves and natural 

 arches, and, in another, broken into wild and insulated pin- 

 nacles. In the botany of the two sides of the valley, we have 



