886 STRATIGRAPHICAL GEOLOGY. [Book VI. _ 
Sweden. When the ice descended into the basin of the Baltic and 
the plains of northern Germany, it moved southwards and south- 
westwards, but seems to have slightly changed its direction in 
different areas and at different times. Its movements can be made 
out partly from the striz on the solid rock, but more generally from 
the glacial drift which it has left behind. Thus it can be shown to 
have moved down the Baltic into the North Sea. At Berlin its 
movement must have been from east to west. But at Leipsic, as 
recently ascertained by Credner, it came from N.N.W. to 8.8.E., 
being doubtless shed off in that direction by the high grounds of the 
Harz Mountains. Its southern limit can be traced with tolerable © 
clearness from Jevennaar in Holland eastwards across the Rhine 
valley, along the base of the Westphalian hills, round the projecting 
promontory of the Harz, and then southwards through Saxony to 
the roots of the Erzgebirge. Passing next south-eastwards along the 
flanks of the Riesen and Sudeten chain, it sweeps across Poland into 
Russia, circhng round by Kieff, and northwards by Nijni Novgorod 
towards the Urals. It has been estimated that, excluding Finland, 
Scandinavia, and the British Isles, the ice must have covered no less 
than 1,700,000 square kilometres of the present lowlands of Europe. 
Some idea of the massiveness of the ice-sheet is obtainable from 
a consideration of the way in which the striz run across important 
hill ranges, and athwart what might seem to be their natural direc- | 
tion. Whilst there was a general southward movement from the 
great snow-fields of Scandinavia, the high grounds of Britain were 
important enough to have their own independent ice, which, as the 
strie show, radiated outward, some of it passing westwards into the 
Atlantic, and some of it eastward into the North Sea. So thick 
must it have been as it moved off the Scottish Highlands that it 
went across the broad plains of Perthshire, filling them up to a 
depth of at least 2000 feet, and passing across the range of the 
Ochil Hills, which at a distance of twelve miles runs parallel with 
the Highlands, and reaches a height of 2352 feet. Many mountains 
in the Highlands are glaciated up to heights of 38000 feet and more, 
while lakes at their feet 600 feet deep have been well ice-worn. It 
has been observed that the strie along the lower slopes of a hill 
barrier run either parallel with the trend of the ground or slant up 
obliquely, while those on the summits may cross the ridge at right 
angles to its course, showing a differential movement in the great 
ice-sheet, the lower parts, as in a river, becoming embayed, and being 
forced to move in a direction sometimes even at a right angle to 
that of the general advance. On the lower grounds, also, the stria, 
converging from different sides, unite at last in one general trend as 
the various ice-sheets must have done when they descended from 
the high grounds on either side and coalesced into one common 
mass. ‘This is well seen in the great central valley of Scotland. 
Still more marked is the deflection of the striae in Caithness and the 
Orkney and Shetland Islands. In these districts the general direc- 
