334 Proceedings of the Royal Physical Society. 



its greatest depth along the stream courses and in the various 

 bays which indent the rocky coast-line. Excellent sections 

 are exposed in the bed of the Forss Water, the Thurso river, 

 at Scrabster Harbour, in Wick Bay, and Dunbeath Water. 

 In many places it reaches a depth of 40 feet, and at Scrabster 

 Harbour its thickness is upwards of 100 feet. In the undu- 

 lating dome-shaped tracts it thins out to a foot or so in 

 thickness, and in many places it disappears altogether. 



We have little to add to Mr Jamieson's accurate account 

 of the physical characters of this deposit. Again and again 

 we had occasion to confirm many of the observations recorded 

 in his paper. We shall therefore have to repeat the descrip- 

 tion of some of the well-known features dwelt on by him in 

 order to show that they cannot be satisfactorily explained by 

 the theory of floating ice. 



The shelly boulder clay is of a dark-grey slate colour 

 when moist, but frequently, in the upper part of the sections, 

 it assumes a brown or ferruginous tint, which may be due to 

 oxidation. It is evident that this brown tint is a mere sur- 

 face discoloration, because when the deposit is dug into for 

 a little way the slate colour appears. Throughout it consists 

 of an extremely stiff gritty clay, charged wdth stones of 

 various sizes. In all the sections the stones are scattered 

 irregularly through the matrix. Occasionally lenticular seams 

 of sand occur in the midst of the deposit, but their presence 

 does not impart a stratified arrangement to it. Indeed, all 

 those who have carefully examined the sections agree in 

 stating that this shelly drift has no trace of stratification, 

 and that in physical character it resembles ordinary Scotch 

 till. Marine shells in a more or less fragmentary form are 

 scattered irregularly through the gritty matrix as well as the 

 seams of sand. There is one section described by Jamieson, 

 on the south side of Wick Harbour, which is of importance, 

 as it shows a slight change in the character of the deposit in 

 the upper parts of the cliff. The section is about 50 feet 

 high, the lower part of which consists of a dark-coloured and 

 very tough gritty clay, with very small stones and numerous 

 remains of marine shells. Thin seams of sand are mixed 

 with this deposit, but there is no trace of stratification. In 



