XVI PREFACE. 



also mentioned that there is a difference, and this sufficient to 

 attract the notice even of the most superficial observer. For 

 instance, the Arenaria verna grows among the unstratified trap 

 rocks of " the head " in the most beautiful luxuriance, while, 

 on the opposite side of the valley, though the distance in one 

 place be nt more than a few yards, not a specimen is to be 

 seen. The Hypericum humifusum, again, we observe in con- 

 siderable abundance on the stratified side, while, on the other, 

 we do not meet with it, and the same remark I have made in 

 similar situations elsewhere. It may be curious also to ob- 

 serve, that the Primula elatior* as well as the common Cow- 

 slip, although abundant among the rocks on the greywacke 

 side, are not met with among those of the opposite side, a re- 

 mark which holds good in other parts of the district compre- 

 hended in the following Flora. 



" Two additional remarks shall conclude our notice .of St 

 Abb's. To the most trivial observer, it must be evident that 

 originally St Abb's Head has been an island of the sea, similar 

 to the Bass in the Frith of Forth, or to the rock of Ailsa in 

 the Frith of Clyde ; it being quite clear, that the sea, at one 

 time, has flowed through the narrow valley, but has gradually 

 been excluded by the debris falling from each side, which has 

 thus elevated its bottom at either end, and united at length 

 St Abb's to the mainland. 



" The other remark relates to the probable origin of that 

 great mass of trap rocks which forms this lofty promontory. 

 It is impossible, we conceive, for any man who knows any 

 thing about rocks at all, to remark the singular position of the 

 greywacke at the little inlet already mentioned, where the two 



* Rather a variety of Primula vulgaris. See p. 54. 



