336 The American Geologist. May, 1891 
perhaps the one of greatest interest relates to the extent of the 
ice-sheets of the British Isles and continental Europe during the' 
latest Glacial epoch. Professor Geikie recognizes certainly two 
and probably three or more epochs of glaciation, between which 
the ice was melted awa} T and as genial climate prevailed as now. 
"Whereas at the time of maximum glaciation, the British ice-sheet 
reached south to the vicinity of London, its latest extension was 
only to Lincolnshire ; but Scotland was wholly ice-covered during 
both of these epochs, excepting only its highest mountain peaks. 
A map of the latest Scandinavian ice-sheet was displayed, repre- 
senting Norway and. Sweden as enveloped by ice, excepting a con- 
siderable part of Gothland in southern Sweden. Eastward this 
ice-sheet appears to have extended to the White sea and to the 
northwestern borders of lakes Onega and Ladoga and of the gulfs 
of Finland and of Riga ; while a hook-shaped broad lobe, called the 
" great Baltic glacier," occupied the area of the Baltic sea, ex- 
tending south into northern Germany and west over about half of 
Denmark. Well defined moraines on the extreme borders of the 
glacial drift in Europe are rare, as they are likewise in the Missis- 
sippi basin of the United States ; but in both countries the more 
limited region of the last glaciation is bounded b} r moraines^ some 
of which have been traced in Great Britain by the late Prof. H. 
C. Lewis, and in Germany by Prof. R. D. Salisbury, both being 
observers who had examined portions of the terminal moraines of 
the United States before going to Europe. 
In the closing lecture the causes of the Glacial period were con- 
sidered. Prof. Geikie believes that the astronomic theory of the 
late Br. Croll, referring the glacial climate to eccentricity of the 
earth's orbit, with accompanying favorable geographic condi- 
tions, is more probable than the explanation that was advanced 
long ago by Lyell and Dana and has been urged anew recently by 
Upham and LeConte, ascribing the ice accumulation to great 
elevation of the land and changes in the course of oceanic cur- 
rents. According to the former theory the Ice age terminated 
about 80,000 years ago. The latter theory, however, is capable 
of accounting for the late glaciation of the northern United States, 
which, according to the careful estimates of N. H. Winchell, An- 
drews, Gilbert, and Wright, from the amount and rate of post- 
glacial erosion in different and widely separated localities, was 
only brought to an end some 7,000 to 10,000 years ago; or in- 
deed it can equally account for the still more recent glaciation of 
the Sierra Nevada and other Cordilleran ranges, which Russell 
and Becker believe to have occurred much nearer to our own 
times. Professor Geikie entirely distrusts these estimates of the 
length of postglacial time ; and the formerly great altitude of both 
North America and Europe, which is proved by fiords and by 
river valleys now submerged 2,000 to 3,000 feet beneath the sea, 
he would refer to geologic periods previous to the Ice age. 
