1 88 The American Geologist. March, 1904. 
geology and physiography. Assuming the early geological cli- 
mates to have been as they are now, governed by solar radiaton, 
he shows that in the cooling^ ol a heated srlobe the iirst part to 
become cool enough to be habitable was at the pole. This is the 
central idea of the treatise. If it should appear that the early 
geolosrical climates were not sun-controlled, but earth con- 
trolled, according to the theory of Manson, and the sun's rays 
were excluded by an encompassing mantle of cloud, it is prob- 
able, as admitted by the author, that all parts of the earth would 
arrive at about the same time to so cool a condition as to be life- 
bearing. The author dismisses this idea as absurd, the mere 
statement of which furnishes its own refutation. 
The author of each of these treatises leaps from "origin of 
life at the pole" to the discussion of the migrations of Tertiary 
and Pleistocene life, apparently not sufficiently realizing that 
the later migrations, which are now well known to have been 
from north to south, may have had no relation to earlier migra- 
tions, and do not at all show the place of the beginning of life 
on the globe. There was an immensely long period, constitut- 
ing far the larger part of geological history as marked by pale- 
ontology, which is thus omitted from the discussion. Whether 
those earliest migrations were governed by the slowly south- 
ward cooling surface, and moved from north to south under 
that impulse we do not know. There are indeed some evi- 
dences that in the Devonian as well as in the Carboniferous the 
Arctic was as well adapted to the fossils characteristic of those 
systems as was the temperate zone. The same is true of the 
Tertiary. Indeed, so far as known, it is true of all the earlier 
ages, i.e. in general terms. Professor Wortman, however, finds 
that comparative studies of the temperate and arctic plants and 
animals indicate a gradual change from tropical and subtrop- 
ical to temperate climate progressive from north to south, up 
to the Glacial epoch. The great migration southward at the 
time of the Glacial epoch, accompanied by the annhilation of 
many species, has a special cause and can hardly be taken into 
the same category. Yet it is the later, and the latest, of these 
movements that the authors appeal to chiefly to prove that life 
began at the pole and spread therefrom over the contitnents. 
There is apparently in the argument an instance of non-sequi- 
tiir — although perhaps a probability on the assumption of iden- 
