BY R. M. JOHNSTON, F.L.S. 115 
the Southern Hemisphere would be comparatively un- 
affected.” 
_ Now from these considerations it is important to observe 
that, as regards Australasia, the influence of geographical 
barriers may be said to be zz/, and that to this region, whatever 
great general climatic changes may have taken place, can be 
referred with greater certainty to astronomical causes alone. 
But if we admit this, we must also allow that the major 
astronomical cause must produce the major effect. Seeing, 
therefore, that Dr. Croll has calculated the amount of eccen- 
tricity of the earth’s orbit 850,000 years ago to be 28°57 per 
cent. greater than during the last cycle which is supposed to 
correspond with the glacial epoch of the Northern Hemi- 
sphere, ought we not to expect to find in Australasia, where 
alone the purely astronomical effect would be most clearly 
revealed, the most marked extreme of climate? If we reason 
correctly we must answer in the affirmative, whatever may 
be our preconceptions, which are ever too prone to take side 
lances at consequences before making a reply. We must 
therefore, in Australasia at least, expect to find, probably near 
to the close of the tertiary period (according to the very 
moderate estimate of geological time by Dr. Wallace), evi- 
dences of a greater intensity of refrigeration of climate than 
during the period corresponding to the glacial epoch of the 
Northern Hemisphere, whose intensity there is mainly due 
to combined causes. The evidences of our rocks by which the 
most competent geologists of Australasia were originally led 
to place our glacier epoch in the pliocene period, and a great 
pluvial epoch in the pleistocene period, are remarkable as a 
confirmation of the potency of the astronomical cause in itself 
to produce at periods of maximum eccentricity great climatic 
changes, corresponding in effect to the degree of eccentricity 
at the respective periods. 
Of course it is taken for granted that the astronomical cause, 
even although operating in a broadly contemporaneous manner 
in both hemispheres in any one epoch, must nevertheless, in its 
minor phases of variation every 10,500 years due to precession, 
place the scene of greatest severity in either hemisphere con- 
secutively and not contemporaneously. 
It is admitted that a glacial epoch is broad enough to 
contain many of such consecutive alternations. 
THe Weicut or NreGativE EVIDENCE. 
The weight of negative evidence against the astronomical 
theory by itself, as regards the absence of glacial deposits in 
other tertiary formations, is ably summarised by Dr. Wallace 
in the following terms :—‘ But when we proceed to examine 
_ the tertiary deposits of other parts of Europe, and especially 
