176 



NOTES OX TH5 GEOLOGY OF EAST LOTHIAN AND BERWICKSHIRE, 



cave^ into which the roar of the waves came with a hollow and sepulchral 

 voice, and the sea-birds swept shrieking around its mouth. This cave is in 

 the Clay-slate and Schists of the Laramermuirs, where they are undermined 

 by the sea. In the interior the Slates are traversed by innumerable and 

 very beautiful Quartz veins; and we were sorry that from the want of 

 instruments sufficiently heavy, we could not procure specimens so fine as we 

 desired. In looking out to sea we observed that the entrance of the cave 

 is characterized by a gorge of the same width with itself, but apparently of 

 great depth, up which the sea came rolling and tossing, as if anxious to lick 

 the sides of the interior, and jealous of its privacy being broken in upon by 

 any intruder; and by its fury it was here dashed into a foam rivalling the 

 snow in purity, and so thick that a small wand might almost have stood 

 erect in it. It was a scene which every true lover of nature must have 

 admired and enjoyed. This cave is a famous breeding- place of the Rock 

 Pigeon, (Columba livia;) and the roof was almost as full of last year's nests 

 as of Stalactites. 



In coming out of the cave, we observed that the Old Red Sandstone lay 

 unconformably to the Clay- slate; indeed the object of our first visit was for 

 the purpose of studying and examining this phenomenon. Strata are said to be 

 unconformable, when one series is so placed over another, that the planes of 

 the superior repose on the edges of the inferior. In this case it is evident 

 that a period had elapsed between the production of the two sets of strata, 

 and that during this interval the older series had been tilted and disturbed. 

 Afterwards the upper series was thrown down in horizontal strata upon it. 

 If these superior beds are also inclined, as they are very considerably, it is 

 plain that the lower strata have been twice displaced; first before the depo- 

 sition of the newer beds, and a second time when these same strata were 

 thrown out of the horizontal position. 



a. o.— Twisted strata of the Silurian Schists. 

 b. b. 6.— Unconformable strata of Old Red Sandstone at Siccar Point. 



Playfair has remarked that this kind of junction, which we now call 

 unconformable, had been described before the time of Hutton, but that he 

 was the first geologist who appreciated its importance, as illustrating the high 

 antiquity and great revolutions of the globe. He had observed that where 

 such contacts occur, the lowest beds of the newer series very generally consist 

 of a breccia or conglomerate, consisting of angular and rounded fragments, 

 derived from the breaking up of the more ancient rocks. ^^On one occasion," 



