1874.] Climate of the Glacial Period. 423 
America that the ice extended farthest towards the equator 
in the Glacial period. 
When Lyell first propounded his theory geologists were 
very imperfectly acquainted with the facts that were to be 
explained, and it was thought that if it could be shown that 
by an alteration in the configuration and distribution of 
land, and a change in the direction of the currents of the 
ocean, icebergs might be floated down to the latitude of 
London, lowering the temperature as they do now in South 
Georgia in lat. 54° S., so as to allow of a perpetual covering 
of snow and the existence of glaciers on the higher grounds, 
a satisfactory solution of the problem would be arrived 
at. But in the half century that has nearly passed since then 
our conceptions of the extent of the ice of the Glacial period 
have slowly but greatly expanded, and we know now— 
although many English geologists still close their eyes to 
the evidence—that the problem to be solved is not one of 
icebergs floating over submerged lands, but a vast piling up 
of ice and snow around the poles, that accumulated until it 
flowed outwards over the existing continents. Let us trace 
this great ice-sheet round the northern hemisphere, as we 
are now nearly enabled to do by the latest observations on 
its extent in northern Asia. 
Commencing in North America, we learn from Dana and 
other eminent American geologists that to the north of the 
St. Lawrence the ice was at least 12,000 feet, or 24 miles, 
in thickness; in the northern parts of New England was 
over 6000 feet in thickness, and, gradually thinning south- 
wards, reached in the lower grounds the parallel of 39° N. in 
the southern parts of Pennsylvania, Ohio, Indiana, Illinois, 
and Iowa, whilst along the mountain ranges local glacier 
systems reached in the tropics at least as far as Nicaragua, 
where within 13 degrees from the equator I found undoubted 
traces of glacier action reaching to 2000 feet above the 
sea-level, where snow now never falls. 
Coming eastward we find, in Nova Scotia and Newfound- 
land, everywhere evidence that they were completely over- 
whelmed with ice. Iceland, according to Robert Chambers, 
is scored across from one side to the other, and was buried 
in ice that may have reached the British Isles, for the 
Hebrides and the north-eastern extremity of Scotland were 
overflowed by ice that came from that dire¢tion. ‘This ice, 
overflowing Caithness, joined by great streams from Scandi- 
navia, and further reinforced by glaciers from the mountains 
of Scotland and the north of England, pushed down the bed 
of the German Ocean, reached as far as the coasts of 
