Mess7's Peach and Home on the Glaciation of Caithness. 335 



the upper part of the section the deposit is of a brownish 

 tint, and less compact. A few feet from the top of the 

 section there are some large blocks of granite, sandstone, and 

 various metamorphic rocks, which are distinctly ice-worn. 

 The occurrence of these blocks, however, is quite exceptional. 

 Along the cliffs to the south of Wick the same change in 

 colour is observable, but fragments of shells are also met 

 with in this material, and the stuff is quite homogeneous 

 from top to bottom. 



The nature of the stones embedded in the deposit deserve 

 special attention, as they furnish important evidence regard- 

 ing the ice movement. Throughout the area the prevalent 

 ingredients are, of course, blocks derived from the underlying 

 Caithness flags. It is particularly observable that in the 

 sections along the eastern seaboard there is a comparative 

 absence of ordinary-sized blocks of this material Indeed, 

 with certain exceptions, the deposit is not stony, as the 

 matrix contains only small well-rounded pebbles. When the 

 sections are followed inland, however, the stones derived from 

 the Flagstone series increase both in number and size. This 

 feature is satisfactorily explained on the supposition that the 

 shelly boulder clay of the eastern seaboard was mainly com- 

 posed of the pebbly silt and sand lying on the bed of the 

 North Sea, which was gradually mingled with materials 

 obtained from the flagstones as the ice advanced inland 

 towards Thurso and Eeay. The presence of the large blocks 

 of flagstone in the upper part of the sections exposed round 

 Wick Bay may be accounted for in the same manner. It is 

 probable that the ice took some time to remove the silt from 

 the sea bottom, and it was not till it had done so that it 

 was enabled to quarry the underlying rocks out of which 

 to manufacture boulders. Dr Penck has explained similar 

 phenomena met with in the Danish drifts in the same way. 

 We frequently noted that the larger blocks of the flagstones 

 lay with their long axes parallel to the direction of the ice- 

 flow, while they are invariably striated in the same direction. 

 This feature was observed by Jamieson in the Milton and 

 Haster burns, and it is capitally displayed in the sections in 

 the Thurso river, between Dirlot and Strathmore Lodo-e. 



