Travers.—On the former Warmth in high Northern Latitudes. 471 
He further alleges, that in the latter case the effect of the trade winds 
would be to impel the heated currents of the Atlantic and Pacifie Oceans 
further towards the North Pole, thereby causing the ice within the arctic 
regions to disappear, and so producing a climate sufficiently mild to admit 
of the existence in those regions of a fauna and flora as rich and varied as 
that which characterized them during any past geological period. 
In the nineteenth chapter of his work he gives a diagram showing the 
eccentricity of the earth’s orbit for 8,000,000 of years in the past, and 
1,000,000 of years to come, at periods of 50,000 years apart, and tables 
showing those matters more in detail at intervals of 10,000 years. On 
looking over the diagram it will be seen that there were three principal 
periods in the past during which the eccentricity rose to a high value. It 
is to one or other of the last two that Mr. Croll assigns the geological period 
familiarly known as the glacial epoch, .preferring, however, the later to the 
earlier one for reasons into which he enters at some length. 
The later period consisted of two separate maxima, the earlier one being 
the greater of the two, and separated from the latter extreme by an interval 
during which the eccentricity was considerably diminished although still 
comparatively high, the whole period occupying 160,000 years, one-half of 
which would represent the united length of the cold phases in each hemis- 
phere. Now, assuming Mr. Croll's views to be correct, the glacial epoch 
which was brought about by this condition of things would continuously 
affect each hemisphere alternately for a period of about 10,500 years, owing 
to the precession of the equinoxes. . But the operation must have been com- 
plicated by the circumstance that, during the 160,000 years in question, there 
was a period of lesser eccentricity occupying some 80,000 years, during which 
the intensity of the cold would have been diminished in each hemisphere. 
It will be observed therefore that, during the period referred to, the con- 
ditions requisite, according to Mr. Croll’s theory, for the production and 
removal of glacial conditions in the northern hemisphere would have 
occurred with varying intensity at alternating intervals of 10,500 years 
about four times, owing to the precession of the equinoxes, or, in other 
words, that the arctic circle would, at the intervals referred to, alternately 
haye enjoyed atmospheric conditions which would admit of the existence of 
a luxuriant fauna and flora, or such as were utterly opposed to the existence 
of any terrestrial life. 
But a glance at Mr. Croll’s diagram will, I think, sufficiently show that, 
whilst his theory may abundantly account for an extension of pre- -existing 
glaciated conditions in each hemisphere during periods of maximum eccen- 
| trieity, there is nothing in it to lead to the conclusion that the polar ice has 
ever been completely removed since its first formation i 1n mass, which, as I 
