332 Proceedings of the Royal Physical Society. 



becomes dark grey, blocks of the secondary rocks make their 

 appearance, and organic remains are abundantly met with. 

 Indeed this latter deposit occurs in great force in the Dun- 

 beath Water, as described by Dick and Jamieson. In the 

 Berriedale Water, however, which drains the northern slopes 

 of Morven and the Scarabens, there are high banks of the 

 reddish-brown ground-moraine, resembling in every respect 

 the sections between Langwell and the Ord. Mr Jamieson 

 states that he observed in the Berriedale Water sections some 

 of the dark blue-grey stuff commingled with the red boulder 

 clay, in which, after some search, he found " nine or ten small 

 pieces of shell and a bit of a Balanusr * But this commingling 

 of the separate deposits occurs near the margin of the shelly 

 drift, where the conflicting ice-streams must have shifted 

 their ground, according to the relative pressure, which need 

 not necessarily have been constant. Such an admixture of 

 the ground-moraine of the respective ice-streams is just what 

 might be expected under these conditions. 



We can now explain the overlap of the dark-grey shelly 

 drift on the red conglomerates, grits, and flags north of Berrie- 

 dale towards Dunbeath, referred to by Mr Jamieson. A 

 similar overlap occurs at the Sarclet, five miles south of 

 Wick, where the same conglomerates and red flags are brought 

 to the surface by means of an anticlinal fold. It is evident 

 that this overlap is due to the forcible invasion of that area 

 by the ice from the North Sea, which pushed along under- 

 neath the mass the pebbly silt and sand charged with marine 

 shells lying in its path. 



Again, in Strathmore, on the banks of the Thurso river, 

 this reddish-brown boulder clay is exposed above Strathmore 

 Lodge. At the bend above the lodge, close by the footbridge, 

 there is an excellent section of this deposit on the right bank 

 ,of the stream. It consists of red gritty boulder clay, with 

 well-striated stones, which have been derived from the meta- 

 morphic rocks to the west. But not far below the lodge the 

 dark-grey shelly boulder clay makes its appearance simul- 

 taneously with the change in the trend of the ice-markings, 



* Quart. Jour. Geol. Soc, vol. xxii., p. 270. 



