Messrs Peach and Home on the Glaciation of Caithness. 349 



deposits of tliis nature, the one comprising local rocks and 

 produced by local ice ; while the other is richly charged with 

 marine shells, and contains blocks which are foreign to the 

 county. The areas occupied by the two boulder clays cor- 

 respond with the limits of the respective ice-streams, as 

 indicated by the striations on the rock surfaces. Moreover, 

 in spite of the lithological uniformity which prevails through- 

 out the tract occupied by the Caithness flagstones, there are 

 certain data connected with the dispersal of the stones in the 

 shelly boulder clay which are only explicable on the supposi- 

 tion that the ice came from the south-east. Blocks of the 

 Sarclet conglomerate can be traced inland in the boulder clay, 

 while striated blocks of the grey flagstones occur in the 

 moraine profonde west of the fault at Brough. Had the 

 movement been from the north-west, then assuredly we 

 would have found material derived from the massive yellow 

 sandstones at Dun net Head in the ground-moraine to the 

 south-east of the fault. But this is not the case. In addition 

 to this, there are blocks of oolitic limestone, oolitic breccia, 

 septarian nodules, fossil wood, belemnites, chalk, chalk-flints, 

 etc., in the shelly boulder clay, some of which are identical 

 in lithological character and fossil contents with the repre- 

 sentatives of these rocks in the basin of the Moray Firth and 

 adjoining tracts. The occurrence of these foreign blocks in 

 the grey drift is not explained by a movement from the 

 north-west, while it is quite in keeping with the theory that 

 the ice which filled the basin of the Moray Firth was 

 deflected and forced to overflow the Caithness plain. In 

 view of all these lines of evidence it is impossible to resist 

 this conclusion. 



When we consider the physical character of the reddish- 

 brown boulder clay, it so completely resembles the ordinary 

 lower till of Scotland, that no one who believes in the land- 

 ice origin of boulder clay would hesitate to ascribe it to the 

 action of that agent. The features presented by the sheUy 

 drift are somewhat different as we have shown, and for this 

 reason the question of its origin has given rise to some 

 diversity of opinion. But a careful consideration of the 

 various phenomena connected with it shows that there is 



