Cause of the Glacial Period 
I gratefully appreciate the suggestions of Mr. Warren Upham in reference to the greater extension 
of the emergent land in the North Atlantic area than is shown on my map. I also concur with him 
that the greater elevation of the land of the American Continent had more effect in bringing about glacial 
conditions in that region, than the reduced temperature of the Gulf Stream, which would have a more 
direct effect upon the climate of Western Europe and the British Isles. 
The views stated by the Rev. G. Crewdson seem to me well worthy of consideration, though the 
subject they open out is too extensive to be discussed here.. The depression of the North-Western 
American Continent during the elevation of the north-eastern side of the same continent may be accepted 
as an all but proven fact; and the entrance of large masses of comparatively warm and moist Pacific 
waters by the enlarged Bering Strait would doubtless have resulted in abundant snowfall on the 
Arctic land areas. On the general question regarding the reciprocal movements of the land on alternate 
sides of the American Continent the recent paper by Professor J. W. Spencer on “ Great Changes of Level 
in Mexico and the Interoceanic Connections” (referred to above) has thrown much light. 
I have been much interested by the views of the Rev. R. A. Bullen, in which I fully concur, and 
am glad to have the support of an observer who has paid so much attention to the physical conditions 
of the North Atlantic. 
The observations of Cav. W. P. Jervis are of much interest and very gratifying. I have had 
several letters of acknowledgment expressing interest in the subject of my paper from Continental 
geologists, including Professor Dames of Berlin, Dr. C. Barrois of Lille, Professor Suess of Vienna, and 
Professor Geinitz of Dresden, and this of Cav. Jervis of Turin is a welcome addition to the list. The 
statement that Issel has traced old river-courses to great depths in the Mediterranean in prolongation of 
valleys in North Italy is dealt with already (Chap. VII.), and is confirmatory of the results arrived at by 
the late Admiral Spratt, where he proved by soundings the existence of a river-channel joining two of 
the lakes formed in the Mediterranean basin between Sicily and Africa during the period of upheaval 
and low water-level. (See Quart. fourn. Geol. Soc. Lond. vol. xxiii. p. 292.) The existence of this 
channel shows the bed of the Mediterranean to have been upraised over 150 fathoms (goo-1000 feet) at 
this period. 
THE END 
Printed by R. & R. Cuarx, Limrrep, Edinburgh. 
