Vol. 62.] GLACIAL PEPvIOD IN ABEKDEENSHIRE, ETC. 31 



eastward up the hollow traversed by the railway between Mulben 

 and Keith. The rocks along this hollow are not of sandstone, but 

 consist of quartz-rock and clay-slate, which give rise to Boulder- 

 Clay of a grey colour, quite distinct from the red. These rocks 

 are covered therefore by grey Drift, above which the red is some- 

 times visible. I traced this red clay as far on at least as Keith, so 

 that the Moray ice must have moved eastward up this hollow. 



At Rothes, a little farther south, and about 12 miles from the 

 coast, we get to the outer edge of the red clay, which has been driven 

 past the boundary of the sandstone. Here a hill called Ben Aigan,. 

 composed of quartz-rock and schist, 1500 feet high, flanks the Spey 

 011 the east. Lying against the northern base of this hill, there is. 

 a high bank bordering the stream and rising about 180 feet above 

 it. This bank affords, or did afford many years ago, a most 

 instructive section. The top consists of well-washed sand and 

 gravel of a greyish colour, much of the sand being so fine as 

 to be blown about by the wind. Beneath that is a great depth 

 of fine stratified silt and sand, of a general gre} T ish colour, in the 

 midst of which, but well down, a mass of red Boulder-Clay makes 

 its appearance, stretching horizontally through the silt from the 

 north, and thinning out to the south in tongues and ribbons, 

 which are more or less interstratified with the grey silt. North- 

 ward, that is to say down the river-side, the red pebbly mud 

 grows rapidly thicker, and occupies the whole depth of the bank, 

 which lowers abruptly owing to the termination of the grey silt in 

 that direction. 



We seem, therefore, to have here the very spot up to which 

 the southern margin of the Moray ice had extended. It had 

 apparently dammed the water and formed a deep pool or lake, in 

 which the sand and mud coming down the flank of Ben Aigan 

 and the Spey was quietly deposited. Here, as in the Valley of the 

 Dee, the local glacier of the Spey appears to have shrunk back long 

 before the thick ice coming from the West Highlands gave way. 

 This harmonizes well with the evidence derived from the Parallel 

 Roads of Glen Boy, which showed that the water of the glacier-lakes 

 of Lochaber found an open way out by the Spey Valley when all the 

 country to the west was still heavily clad with ice. 



Terraces of gravel occur on both sides of the Spey at Rothes, at 

 corresponding heights, the top of them being fully 400 feet above the 

 sea. They also run up the Mulben hollow, where there are deep 

 banks of Drift, in some of which I could distinguish a middle zone of 

 red, with grey material both above and below. When the Moray 

 ice-stream gradually shrank, it must have dammed the river at lower 

 and lower levels. Accordingly we find remnants of gravel- terraces 

 here and there, at decreasing heights as we proceed down the stream, 

 at Cairnty and elsewhere. When I first examined these terraces 

 47 years ago, I thought that they had been caused by the sea, 1 but no 

 marine fossils have ever been found in any of them. These terraces 



1 See Quart. Journ. Geol. Soc. vol. xiv (1858) p. 527. 



