Cause of the Glacial Period 
were acting simultaneously ; and it is to their combined influence that we may ascribe the general 
lowering of temperature, and prevalence of more arctic climatic conditions, of which we have evidence 
during the Pleistocene period. 
Parr IV.—ConcLusion 
The causes which have been assigned for a glacial epoch may be arranged under two heads—the 
astronomical and the terrestrial. Under the former may be placed the theory of the late Dr. Croll, 
which has the support of Professor James Geikie, and that of Sir Robert Ball more recently enunciated ; 
under the latter is that of Lyell, who held that “in determining the climate of the globe geographical 
changes have exercised a preponderating influence.” Croll’s hypothesis has been examined by Lyell, 
Prestwich,? and others, who are unable to accept its conclusions, as well on astronomical as on physical 
grounds. Lyell in the last edition of his great work still adheres to his original views, which find 
support in the conclusions here arrived at. Few will deny that, but for the Gulf Stream, the British 
Isles and Northern Europe would now be subjected to glacial conditions ; and with the aid of Professor 
Spencer’s researches I have attempted to show how such conditions were brought about. 
I must not omit to refer to the view of Mr. Warren Upham, of the United States Geological Survey, 
who has dealt with this subject in an able paper communicated to the Victoria Institute in the session of 
1896-97,® who corroborates generally the views of Professor Spencer, and other American geologists, 
including Dana and Le Conte, regarding the former great uprise of the continental lands at or near the 
commencement of the Glacial epoch ; arriving at similar conclusions to those of the author of this work, 
but based mainly on the view of the lowering of temperature due to such elevation. I have endeavoured 
to show how, in addition to the lowering of temperature due to elevation of land in the Northern Hemi- 
sphere, the deflection of the Gulf Stream must have also materially influenced the climatic conditions. It 
need scarcely be stated that both papers were written altogether independently of each other; but 
their agreement in the conclusions will be regarded as confirmatory of the “epeirogenic” or “ earth- 
movement ” hypothesis. 
The most able opponent of this hypothesis is Professor James Geikie, and I have re-read his elaborate 
communication to the Victoria Institute,! dealing with this subject, in order to refresh my memory as 
regards his views and arguments ; which have also been dealt with by Mr. Warren Upham, and, as it 
seems to me, in the main, successfully.? I cannot see, for instance, upon what ground Geikie considers 
the American uplift to have been long antecedent to the Pleistocene epoch. Of course the uprise of the 
land around the shores of the North Atlantic was gradual, and the accumulation of snow and ice would 
also have been a very slow process; but both Spencer and Upham are agreed that this uprise commenced 
with the close of the Pliocene period ; a view which seems the more reasonable one.® At the same time 
I agree with Professor Geikie in doubting that the oscillations of land of the Pleistocene period were to any 
great extent (if at all) due to the weight of accumulated snow (or its removal), as supposed by Dana. In 
the view of the occurrence of two cold epochs with an intervening warmer (or interglacial) stage, I have 
long been a believer, and maintain that it is borne out by the glacial phenomena of the British Isles, 
as I endeavoured to show many years ago,’ but such movements were probably not dissimilar in their 
origin and cause to those of former geological periods to which the crust of the earth has been subjected. 
1 Principles, vol. i. ch. xii. 2 Geohgy, vol. ii. 
3 Upham, “Causes of the Ice Age,” Fourn. Vict. Inst. vol. xxix. p. 201 (1897). 4 [bid. vol. xxvi. 
5 Ibid, pp. 221 and 254, also vol. xxix. p. 237. 
6 See on this point a more recent paper by Professor Spencer on “The Continental Elevation of the Glacial Period,” Geshgical Magazine, 
January 1898. In this paper the author extends his observations on the great continental uprise to the eastern and northern coasts of the Atlantic, 
suggesting changes regarding the European and British area far in excess of those referred to by myself for these regions." 
7 Physical History of the British Isles, ch. xiii. plates 13 and 14 (1882). 
36 
