84 JOURNAL OF SCIENCE. 
Mr. Wallace seeks to prove by an examination of our flora, and 
by the existing geological conditions of Australia. 
Stated concisely, his conclusions are, that for a long period of 
time Australia was divided into two islands, a western and an 
eastern. In the former of these, the peculiarly characteristic 
Australian genera, both of plants and animals, originated. The 
eastern island stretched in a long narrow line from the tropics to 
the south of Tasmania, and in connection with its tropical portion 
there was probably a prolongation of New Zealand to the north- 
west. By this bridge, with its southerly and south-easterly 
ramifications, a stream of immigrants set in from the tropical 
regions further north, so that numerous genera, and even species 
of plants, as well as some animals, were spread along both shores 
of the sea separating New Zealand from Australia. The subse- » 
quent depression of the northern area caused a separation of New 
Zealand from tropical Australia, while the elevation of the com- 
paratively shallow sea separating the western from the eastern 
island united these two into the great continental island of 
Australia, over the whole of which the peculiar western forms 
spread rapidly, and apparently at a much greater rate than the 
tropical and eastern species did. While the presence of the 
Australian, Asiatic, and Polynesian elements in the New Zealand 
flora are traceable tu this former land connection, the antarctic 
and South American forms are believed to be due to immigration 
from outlying islands and extensions of land to the South, and the 
European, or more correctly the arctic, element is explained by 
the extraordinarily aggressive character of the so-called Scandi- 
navian flora, which has enabled it to push its colonists over the 
three great southern areas—viz, South Africa, South America, 
and Australasia. 
Mr. Wallace’s explanations of the origin of our flora must 
commend themselves as extremely satisfactory to every one 
capable of judging of the questions under consideration. Our 
subsequent knowledge may modify some of his conclusions to a 
slight extent, but it is by the publication of such hypotheses and 
theories, and the application of them for the solution of difficult 
problems, that correct ideas are most rapidly attained. Not only 
is our interest heightened by such speculations, but definite issues 
are placed before our minds, and we are enabled to judge more 
and more accurately of these, and to recognise how vast the field 
to be traversed is. It is well to bear in mind that, as our stock of 
tacts increases, so also does our knowledge of our ignorance, and 
that the latter often increases in a much more rapid ratio than the 
former. We begin by discussing a limited question, satisfied 
perhaps that we have sufficient information accumulated to enable 
us to give a definite answer, but at every turn collateral points are 
raised, until at last we feel ourselves tace to face with an over- 
powering mass of questions all demanding solution, and areat the 
same time conscious of our inability to grapple with them. Butit | 
is only given to the tew—to a very limited few indeed—to be able 
to generalize and build up into a homogeneous whole the hetero- 
geneous materials collected by the multitude. We can all help to 
accumulate these materials together, leaving it to the master- 
minds of science to use the fruits of our labours. 
I have very briefly attempted to show what are the principal . 
