_ Prof. James Geikie’s Address. 465 
clay, with stones scattered irregularly through it. Such being the 
ease in modern glaciers, we can hardly doubt that over the peripheral 
areas occupied by the old northern ice-sheet Boulder-clay must 
frequently have been accumulated in the same way. Nay, when the 
ground-moraine melted out and dropped here and there into quietly- 
flowing water, it might even acquire in part a bedded character. 
The limits reached by the inland ice during its greatest extensions 
are becoming more and more clearly defined, although its southern 
margin will probably never be so accurately determined as that of 
the latest epoch of general glaciation. The reasons for this are 
obvious. When the inland ice flowed south to the Harz and the 
hills of Saxony it formed no great terminal moraines. Doubtless 
many erratics and much rock-rubbish were showered upon the surface 
of the ice from the higher mountains of Scandinavia, but owing to 
fanning-out of the ice on its southward march such superficial debris 
was necessarily spread over a constantly widening area. It may 
well be doubted, therefore, whether it ever reached the terminal 
front of the ice-sheet in sufficient bulk to form conspicuous moraines. 
It seems most probable that the terminal moraines of the great inland 
ice would consist of low banks of Boulder-clay and aqueous materials 
—the latter, perhaps, strongly predominating, and containing here 
and there larger and smaller angular erratics which had travelled on 
the surface of the ice. However that may be, it is certain that the 
whole region in question has been considerably modified by sub- 
sequent denudation, and to a large extent is now concealed under 
deposits belonging to later stages of the Pleistocene period. The 
extreme limits reached by the ice are determined rather by the 
occasional presence of rock strie and roches moutonnées, of Boulder- 
clay and northern erratics, than by recognizable terminal moraines. 
The southern limits reached by the old inland ice appear in this 
way to have been tolerably well ascertained over a considerable 
portion of Central Europe. Some years ago I published a small 
sketch-map ! showing the extent of surface formerly covered by ice. 
On this map I did not venture to draw the southern margin of the 
ice-sheet in Belgium further south than Antwerp, where northern 
erratics were known to occur; but the more recent researches of 
Belgian geologists show that the ice probably flowed south for some 
little distance beyond Brussels.? Here and there in other parts of 
the Continent the southern limits reached by the northern drift have 
also been more accurately determined, but so far as I know, none of 
these later observations involves any serious modifications of the 
sketch-map referred to. 
I have now said enough, however, to show that the notion of a general 
ice-sheet having covered so large a part of Europe, which a few 
years ago was looked upon as a wild dream, has been amply justified 
by the labours of those who are so assiduously investigating the 
peripheral areas of the ‘‘ great northern drift.” And perhaps I may 
be allowed to express my own belief that the drifts of Middle and 
1 Prehistoric Europe, 1881. 
2 See a paper by M. E. Delvaux, Ann. de la Soc. géol. de Belg. t. xiii. p. 158. 
DECADE I1I.—VOL. VI.—NO. X. 30 
