BY R. M. JOHNSTON, F.L.S. 79 
clay, sand, gravel, or drift which can be traced more or less 
directly to glacial action. Some of these are moraine matter, 
others are lacristrine deposits, while others again have been 
formed or modified by the sea during periods of submergence. 
But below them all,and often resting directly on the rock 
surface, there are extensive layers of a very tough, clayey 
deposit known as the ‘till.’ The till is very fine in texture, 
very tenacious, and often of a rock-like hardness. It is 
always full of stones, all of which are of rude form, but with 
the angles rubbed off, and almost always covered with 
scratches and striz, often crossing each other in various 
directions. Sometimes the stones are so numerous that there 
seems to be only just enough clay to unite them into a solid 
mass; and they are of all sizes, from mere grit up to rocks 
many feet in diameter. The ‘till’ is found chiefly in the 
low-lying districts, where it covers extensive areas sometimes 
to a depth of a hundred feet, while in the Highlands it occurs 
in much smaller patches, but in some of the broader valleys 
forms terraces which have been cut through by the streams. 
Occasionally it is found as high as two thousand feet above 
the sea, in hollows or hill sides, where it seems to have been 
protected from denudation.” The “till” is totally unstrati- 
fied, and the rock surfaces upon which it almost always rests 
are invariably worn smooth, and much grooved and striated 
when the rock is hard, but when it is soft or jointed it fre- 
quently shows a greatly broken surface. Its colour and 
texture, and the nature of the stones it contains, all corre- 
spond to the character of the rock of the district where it 
occurs, so that it is clearly a local formation. It is often 
found underneath moraines, drift, and other late glacial 
deposits, but never overlies them (except in special cases to 
be hereafter referred to), so that it is certainly an earlier 
deposit. Throughout Scotland where “till” is found the 
glacial strise perched blocks, roches moutonneés, and other 
marks of glacial action occur very high up the mountains to 
at least 3,000 and often 3,500 feet above the sea, while all 
lower hills and mountains are rounded and grooved on their 
very summits, and these grooves always radiate outwards 
from the highest peaks and ridges towards the valleys or the 
Sea, 
“ Inferences from the Glacial Phenomena of Scotland —Now 
all these phenomena taken together render it certain that the 
whole of Scotland was once buried in a large sea of ice, out 
of which only the highest mountains raised their summits.” 
“The weight of this vast ice sheet, at least three thousand feet 
in maximum thickness, and continually moving seaward with 
a slow grinding motion like that of existing glaciers, must 
have ground the whole surface of the country, especially all 
