22 
POPULAR SCIENCE REVIEW. 
the tree -vegetation of N ew Holland. Amongst the fossils of the 
Eocene formation we have corresponding with them the genera 
Pterocarpus, Brepanocarpu s, Centrolobium, Dalbergia, Cassia , 
Ccesalpinia , Bauhinia, Copaifera, Entada, Acacia , Mimosa , 
and Inga — Acacia being, perhaps, most numerously repre- 
sented. 
Seeing what a considerable portion of the Australian and 
Polynesian flora was represented by cliar act eristic types in the 
Eocene period, we can no longer entertain any doubt that Europe 
stood in some hind of connection with New Holland. But what 
was the exact nature of this connection ? Let us hear Dr. Unger’s 
answer. Wherever similar or the same effects in natural phe- 
nomena are perceived, we are justified in ascribing them to 
similar or the same causes. A vegetation in Europe bearing 
the same character as that of New Holland and the adjacent 
islands of the present day compels us to admit that, at the 
Eocene period, a set of conditions prevailed in our continent 
similar to those under which the Australian flora at present 
exists. It is not conceivable that when our forests were 
formed by Araucarias, instead of Pines, and our underwood of 
Proteacece , Santalece, &c., instead of Ehammi, Privets, and 
Hazels, the climate and soil should have been the same as 
they are now. We know but too well what peculiar conditions 
of temperature, light, moisture, &c., certain plants require, 
and how slavishly we are tied to certain rules in our cultivation 
of foreign plants. True, Araucarias , Proteacece, and Epacridece 
grow, at present, exceedingly well in Europe, but only when 
protected by glass, in a certain artificial temperature and 
light, and a well-prepared soil — calculated to approximate 
the exceptional conditions under which they are grown to 
those of their native country. We may, therefore, conclude 
with good reason that the conditions which wp produce arti- 
ficially, in order to grow these plants, existed in the whole 
of Europe ; in short that, at the Eocene period, Europe must 
have had a climate like that of New Holland at the present day. 
But by thus determining the climate of Europe during 
the Eocene period, we have not proved more than that our 
part of the world could formerly support a vegetation 
which required a much milder climate. It is more important 
to ascertain how the vegetation of a continent situated 
at our very antipodes could find its way hither. It is com- 
paratively easy to account for the spreading of the plants 
of an adjacent milder climate to our northern zone, or how 
the plants of a northern subtropical region came to us ; but 
the occurrence of representatives of the southern hemisphere 
in the northern certainly demands a very peculiar set of con- 
ditions. In trying to solve this problem we shall have to 
