104 THE GLACIER EPOCH OF AUSTRALASIA. 
with the glacier epoch of Australia in the early Pliocene, and 
the later “ice age” of Europe and North America in 
Pleistocene age, are undoubtedly thus shown to be truly 
exceptional conditions recurring irregularly and not con- 
current with the comparatively frequent cycles of the earth’s 
eccentricity, except at very wide intervals of time, when, pro- 
bably, the peculiar combination of astronomical, physical, and 
geographical causes combined to produce those extreme and 
exceptional conditions, corresponding to the three almost 
universal glacial or cold epochs, of which the rocks contain 
the most abundant and undoubted evidence. 
GuactAL Epocus HARMONISING WITH GREAT CYCLES OF 
CHANGE IN THE Puant Lire or AUSTRALIA AND 
TASMANIA. 
The acceptance of the “exceptional occurrence” view of 
glacial epochs is also strongly corroborated by the great 
cycles of vrganic changes, especially as regards plant life. 
Thus, about the time of the glacial epoch of Permo- 
Carboniferous age, the original flora of Australiaand Tasmania 
consisted, mainly, of the following characteristic genera, 
viz., Glossopteris, Gangamopteris, Noeggarathiopsis, Schizoneura, 
Lepidodendron. 
After the Permo-Carbontferous glacial epoch, correspond- 
ing to the ushering in of the milder Mesozoic age, the 
old flora of Permo-Carboniferous age sudienly died away 
completely. ot a vestige remained! The Mesozoic rocks 
then became almost suddenly characterised by the abundance 
of the following plant forms, viz.:—Pecopteris, Neuropteris, 
Sphenopteris, Thinnfeldia, Cyclopteris, Teniopteris, Odontop- 
teris, Sagenopteris, Alethopteris, Phyllotheca, Annularia, 
Podozamites, Pterophyllum, Otozamites, Sphenozamites, Brachy- 
phyllum, Taxites, Sequottes, Walchia, Cunninghamites, Arau- 
carites, Batera, Salisburia, Ginkgophyllum, Leugophyllites, 
(Poa-cordiates). 
At the close of the Mesozoic age in Tasmania allits rich and 
varied flora in its turn disappeared, or “yielded to the great 
law of death ;’ and although for the most part no marine 
beds intervene between our Upper Mesozoic rocks and the 
immediately succeeding Lower Tertiary leaf beds, the flora of 
the latter were ‘‘ brought to the birth and ushered upon the 
scene” suddenly, and appearing locally as if a new creation. 
But it is significant that this sudden change zs exactly 
zsochronous with an unparalleled eruption of igneous rocks 
(later greenstone) concurrent with widespread convulsions of 
the older strata. These greenstones even now are so wide- 
spread as to form the leading physiographical features 
