Vol. 62.~] GLACIAL PERIOD IN ABERDEENSHIRE, ETC. 23 



that I had noticed a somewhat similar dark clay in a like position 

 in other places, birt not showing any shell-fragments. Thus, in a 

 railway-cutting a few miles south of Ellon, I had observed that the 

 lowermost part of the section was composed of a very dark indigo- 

 coloured clay, in which I found a piece of fossiliferous shale con- 

 taining the impression of a small ammonite, and what seemed to 

 be fish-scales. 



The bottom-clay in the railway-cutting at Belscamphie, on the 

 Cruden line, mentioned on p. 17, is also very like the dark bed at 

 Craigs of Auchterellon. I found, however, nothing remarkable in it, 

 although I did get a crumb or two of what might have been shell, 

 which effervesced on being treated with acid. I could also 

 mention other localities in this quarter, where a very dark bluish 

 clay occurs beneath a Boulder-C]ay of greyer hue. 



I therefore think that there may have been a fairly-widespread 

 dark clay of older date than the grey, and formed by a previous 

 phase of the ice. The action of a thick sheet of glacier-ice moving 

 over the surface of a country would be something like that exerted 

 by a carpet dragged over a floor, and, if long-continued, would leave 

 very little if an} T older loose stuff behind it. Its plastic nature and 

 heavy pressure adapt it so closely to all irregularities of the floor 

 on which it rests, that hardly any place can escape its friction ; and 

 this accounts for the entire absence of all remains of pre-Glacial 

 Tertiary deposits in Scotland. Each recurrence of an ice-sheet 

 would tend to wipe out the material left by its predecessor, especially 

 if the later one was heavy and long-continued. 



Although, then, we have some evidence of more than one re- 

 currence of an ice-sheet in this part of Scotland, no evidence has 

 hitherto been obtained of warm intervals, further than what may be 

 inferred from the melting-away of the vast mass of ice which 

 preceded and followed the deposition of the lied Clay and the shell- 

 beds at Clava and elsewhere. It must have taken a great deal of 

 heat to melt these enormous masses. The deposition of the Eed 

 Clay seems to have followed close upon the retreat of the ice which 

 lodged the grey Boulder-Clay. There is no sign of any interval 

 there; but a long interval, and possibly a warm one, may have 

 occurred between the time of the Eed Clay and that of the later 

 ice-sheet which lodged the Upper Boulder-Clay and gravel. 



The blackish shelly clay at Ellon must, I suspect, have come 

 down the Ythan Valley from the Moray-Eirth direction, and may be 

 of the same age as the dark clay at Maud, to be afterwards mentioned 

 (p. 29), which contains Oolitic fragments and pieces of serpulite- 

 grit from the North-Western Highlands. These latter probably 

 came down the valley of Loch Shin in the great ice-stream which 

 seems to have descended along that route into the Moray Eirth, 

 and pressed on over the southern border of that basin. Their occur- 

 rence in the northern part of Aberdeenshire is a very curious and 

 interesting fact, which we owe to the observation of Mr. John Milne, 

 formerly tenant of the farm of Atherb. 



