1894 THE MICROSCOPE. 161 



quartz — that is, of absolutely unqualified or unadulter- 

 ated oxide of Silicon — for that is what quartz really is 

 — we should be able to learn very little regarding their 

 previous history. The shape, size, and surface mark- 

 ings of the grains might tell us a little. When, for in- 

 stance, we come across a grain striated as in figure 2, a 

 striated grain of quartz from Boulder Clay, our thoughts 

 at once go out to glaciated boulders and the Ice Age. It 

 is like a miniature glaciated boulder, and is sufficiently 

 realistic to give one a cold shiver. It is from the pit of 

 Boulder Clay behind the Morayshire Combination Poor- 

 house, and many more — perhaps not all so finely marked 

 — are to be found among the quartz grains of the 

 Boulder Clay. As many as 15 per cent I find from my 

 analyses are described under the heading " Striated." 

 No doubt the friction of sand particles against one 

 another under water causes many indefinite scratchings 

 of their surfaces, but when we get several deep and 

 roughly parallel groovings, such as we have here, I think 

 we are justified in calling in the agency of glacier-ice as 

 a more eflBcient cause. Our sea sand, again, by common 

 consent acknowledged to be largely made up of the wash- 

 ings of old Boulder Clays, shows about 10 per cent of 

 such striated grains ; while among the sandstones they 

 are seen particularly at Scaat Craig, which shows 8 per 

 cent and among ihe rougher beds of jSTewton, 10 per cent 

 of which are also noted as " Striated." The existence of 

 striae in these latter confirms the theory of recurring 

 glacial periods at various times in the remote geological 

 past. One curious result that emerged from amid our 

 maze of figures was the very significant one that a very 

 large proportion of the striated grains are of granitic 

 origin. This is equally true of the recent, as of the early, 

 manifestations of glaciation. The explanation, prob- 

 ably, is that the operations of glacier ice were for the 

 longest period, and in very large measure, confined to 



