336 Froceedinfjs of the Roi/al Physical Society. 



Here there are occasional blocks of grey and chocolate flags, 

 upwards of 3 feet in length, arranged as described. 



Owing to the remarkable uniformity in the character of the 

 Caithness Flagstone series there is some difficulty in deter- 

 ming the direction of the ice-carry from the dispersal of the 

 local rocks in the boulder clay. There is one striking 

 instance, however, to which we paid special attention, which 

 confirms the opinion that the ice must have come from the 

 south-east. The peninsular tract of ground, which is situated 

 between Brough Bay and Dunnet Bay, extending northwards 

 to Dunnet Head, measuring about five square miles in extent, 

 is occupied by coarse yellow and red sandstones, which are 

 brought into conjunction with the Flagstone series by a fault. 

 This dislocation runs from Brough Bay southwards by St 

 John's Loch and the church of Dunnet to Dunnet Bay. 

 Now, in the boulder clay sections to the east of the fault, no 

 trace of these characteristic sandstones is to be seen on the 

 shore or inland, whereas the Caithness flagstones have been 

 carried on to the surface of these Upper Old Pted Sandstone 

 rocks. Had the ice-flow been f 7^771 the north-west, the 

 phenomena would have been precisely the reverse of what 

 we have stated, as blocks of these massive sandstones would 

 certainly have been mingled with the moraine profonde to 

 the south-east of the fault. 



Again, on the shore about four miles to the south of Wick, 

 at the Sarclet, massive beds of conglomerate, attaining a 

 thickness of nearly 300 feet, are brought to the surface by 

 means of an anticline.* Blocks of this conglomerate can 

 be traced inland from this locality, both in the boulder clay 

 and on the surface in the direction of Thurso.-f* 



But in addition to these local rocks there is a large per- 

 centage of blocks which are foreign to the Caithness plain. 

 Amongst these may be mentioned granite, porphyritic felsite, 

 diorite, gneiss, mica schist, quartzite, oolitic limestone, oolitic 

 brecciated conglomerate, grey sandstone belonging to the 



* Trans. Roy. Soc, Edin., vol. xxviii., p. 376. 



+ Dick mistook the boulders of this rock, which he found between Thurso 

 and Dunnet, for fragments derived from the conglomerates of Port Skerry in 

 Sutherlandshire, from which they differ considerably. 



