president’s address. 
1811 
■was strongly impressed with the glacial character of a Silurian 
conglomerate Avhich he found near Temora (David, Q.J.G.S., 
XLiii. p. 195.) 
Farther, it is accepted by most candid incpiirers that Dr. Croll’s 
views as to the Alternation of Extreme and Temperate climates 
in the Xorthern and Southern Hemispheres (Climate and Time, 
p. 75, Chs. xiv.-xviii., tfec.,) are not only theoretically satisfactory, 
but are also borne out by all such evidence as is obtainable. “The 
most important result for us,” says Darwin, “ arrived at by 
!Mr. Croll, is that wherever the Northern Hemisphere passes 
through a cold period, the temperature of the Southern is actually 
raised, with the winters rendered much milder, chiefly through 
changes in the direction of the Ocean currents. So conversely it 
will be with the Northern hemisphere while the Southern passes 
through a glacial jieriod.” (Origin of Species, Ed. vi., p. 336.) 
The rest of chapter xii. is taken up with this argument. 
Wallace, Island Life, p. 151, sq. discusses the same question. It 
results that an Indian Glacial period must be compared with an 
Australian Interglacial, and that only the African and Australian 
(and Soutlj American 1) periods of Glaciation (in any sense of the 
word) can have been contemj)oraneous. We must therefore con- 
fine our attention in the flrst place to the lands south of the 
Equator, in which the course of events during the Carbouiferous 
and Mesozoic periods seems to have been somewhat as follows, 
viz. : — 
Dunng the later Devonian and older Carboniferous there was 
developed in the Holarctic regions, a form of vegetation which is 
known in the Northern Jfeiuisphere as Carboniferous, but which, 
Uj avoid ambiguity, 1 shall call the Lepidodendron flora. Tliis 
gradually extended itself on a restricted scale into the South 
African and Australian regions witliout, as it seems, entering 
the pre.sent peninsula of India, which was at that time disconnected 
from the northern mainlatid, New Zealand, or even Tasmania. 
Eiistern Australia at this period consisted of a chain of islands, 
extending along the line of the present Great Dividing Kang«‘, 
