322 Tropical Zoology. (July, 
the province of Maranham, in Brazil, a great drift deposit 
apparently of glacial origin. Hence, he, very justifiably, 
thinks it highly probable that the ice deposits of the glacial 
period were far more extensive than has been generally 
supposed, existing at once in both the northern and southern 
hemispheres, and leaving, in America at least, only the 
lower lands of the tropics free from the icy covering. 
Were the causes of such a redu¢tion of the earth’s general 
temperature cosmic or merely terrestrial? ‘The author does 
not enter minutely into this question, though, with Professor 
Heer, he considers that the cold of the glacial period, like 
the warmth of the miocene epoch, ‘‘ cannot be explained by 
any re-arrangement of the relative positions of land and 
water.” It is very true that were the circum-polar lands, 
British North America and the Russian empire, deeply sub- 
merged beneath the ocean, and were a corresponding amount 
of land raised where now rolls the inter-tropical Pacific, the 
temperature of the world would be much ameliorated. But 
the very evidence of the heat of the miocene ages,—the 
existence, at that time of the beech, the hazel, and the plane 
in Spitzbergen, in north latitude 78°, proves that the polar 
regions were not an unbroken expanse of water. Similarly, 
the proofs of glacial action within the torrid zone show that 
during the glacial period land was by no means wanting 
between the tropics. It seems, therefore, highly probable, 
that in regarding these alternating epochs of heat and cold, 
‘‘we are face to face with a problem whose solution must 
be attempted, and doubtless completed, by the astronomer.” 
But there is another phase of the subject to which the 
attention of the author is mainly given. Every botanist and 
geologist, on hearing of these enormous ice-deposits in what 
are now some of the most luxuriant climates of the world, 
will ask what must have become of all tropical forms of 
organic life? The very tierras calientes in those days, in- 
stead of towering palms and of epiphytal arads and orchids, 
must have possessed a vegetation little richer than that of 
England or Germany in the present order of things. 
Heliconii and Morphos can never have unfolded their 
delicate wings on the chill blast from the ice-deserts. The 
author meets this difficulty by the hypothesis that “a 
refuge was found for many species on lands now below the 
level of the ocean, but then uncovered by the lowering of 
the sea, consequent upon the immense quantity of water 
locked up in the form of ice, and piled upon the continents.” 
A variety of evidence is adduced in support of this view. 
The distribution of animal life over small islands now 
