322 Proceedings of the Royal Physical Society, 



tion. The geological structure of this tract has been fully- 

 described by Professor Geikie in his elaborate monograph on 

 "The Old Eed Sandstone of Western Europe,"* to which 

 reference may be made for details. Beyond the limit just 

 indicated the strata consist of white quartzites forming the 

 range of the Scarabens (2054 feet), orthoclase gneiss, mica 

 schists, and occasional masses of granite ; but to these we 

 paid no special attention. 



An important feature connected with the glaciation of 

 Caithness is the complete divergence in the trend of the 

 ice-markings, in the area occupied by the shelly boulder 

 clay, and the district lying to the west towards the county 

 boundary. In the former area the prevalent trend is north- 

 west and south-east, which Mr Jamieson and Dr CroU clearly 

 showed could not have been produced by any local radiation 

 of the ice — a conclusion which is self-evident to any one 

 who considers the physical features of the county. In the 

 district lying to the west of this area towards the county 

 boundary, the striae point E., E.N.E., KN.E., K, and even- 

 tually they veer round to the N.W., along the inland margin 

 of the shelly boulder clay. We shall first describe some of 

 the examples met with in the area occupied by the shelly drift. 



In the district between Eeay and Thurso we observed 

 numerous examples on the surfaces of the flagstones. By 

 the roadside west of the granite ridge at the burn of Isauld, 

 striae are seen on the grey flagstones beneath a thin covering 

 of red boulder clay, pointing W. 40° N. These agree with 

 the instances noted by Mr Jamieson at Eeay, running KW. 

 and W. 35° N. At Shebster we observed ice-markings point- 

 ing W. 30° K, and at Westfield, near the Forss Water, W. 20° 

 to 25° N. 



On the surface of the blue flags in the Achscrabster 

 quarries the trend is W. 25° N". This locality is interesting 

 on account of the evidence which it affords of an ice move- 

 ment towards the north-west. Subangular blocks have been 

 broken off the flagstones by the ice in its passage over them, 

 which are tilted at a gentle angle towards the north-west, 

 while the flags themselves have been bent over in the same 



* Trans. Koy. Soc, Edin., vol. xxviii., p. 406. 



