210 James Croll — Boulder-clay of Caithness. 



"The appearance of the drift along ihe Haster Bum, and in 

 many other places in Caithness, is in fact precisely the same as that 

 of the old Boulder-clay of the rest of Scotland, except that it is 

 charged with remains of sea shells and other marine organisms. 



" If want of stratification, hardness of texture, and abundance of 

 well-glaciated stones and boulders are to be the tests for what we 

 call genuine Boulder-clay, then much of the Caithness Drift will 

 stand the ordeal." 



So far, therefore, as the mere appearance of the drift is concerned, 

 it would be at once pronounced to be true Lower Till, the product 

 of land-ice. But there are two circumstances connected with it 

 which have been generally regarded as fatal to this conclusion. 



(1) The stri^ on the rocks show that the ice which formed the 

 clay must have come from the sea, and not from the interior of the 

 country ; for their direction is almost at right angles to what it 

 would have been had the ice come from the interior. Over the whole 

 district, the direction of the grooves and scratches on the rocks is 

 pretty nearly N.W. and S.E. But this is not all, the very stones 

 in the clay are striated in this direction. " When examining the 

 sections along the Haster Burn," says Mr. Jamieson, " in company 

 with Mr. Joseph Anderson, I remarked that the strias on the 

 imbedded fragments generally agreed in direction with those of the 

 rocks beneath. The scratches on the boulders, as usual, run length- 

 waj's along the stones when they are of an elongated form ; and the 

 position of these stones, as they lie embedded in the drift is, as a 

 rule, such that their longer axes point in the same direction as do 

 the scratches on the solid rock beneath ; showing that the same 

 agency that scored the rocks also ground and pushed along the 

 drift." 



Mr. Peach informs me that he seldom or never found a stone with 

 two sets of strige on it, a fact indicating, as Mr. Jamieson remarks, 

 that the drift was produced by one great movement invariably in the 

 same direction. Let it be borne in mind that the ice, which thus 

 moved over Caithness in this invariable track, must either have 

 come from the Atlantic to the N.W., or from the Moray Firth to 

 the S.E. 



(2) The Boulder-claj'^ of Caithness is full of sea-shells and other 

 marine remains. The shells are in a broken condition, and are 

 iiitei'spersed like the stones through the entire mass of the clay. 

 Mr. Jamieson states that he nowhere observed anj- instance of shells 

 being found in an undisturbed condition, '•' nor could I hear," he 

 says, "of any such having been found ; there seems to be no such 

 thing as a bed of laminated silt with shells in situ" The shell- 

 fragments are scratched and ice-worn, the same as the stones found 

 in the clay. Not only are the shells glaciated, but even the 

 FOraminifera, when seen through the microscope, have a rubbed and 

 worn appearance. The shells have evidently been broken, striated, 

 and pushed along by the ice at the time the Boulder-clay was being 

 formed. 



