101 
their continued existence affords ground for most interesting 
speculation and is intimately connected with the history of our 
portion of' the Australian continent. 
The laud surface of south-west Australia is an old one, having 
maintained its position during earth changes which have caused 
other land masses to be raised above or submerged below the ocean 
waters* In addition, through a very great period of time, there 
lias been a continued isolation from other land regions. As a 
result, our flora (and fauna also) has in large measure been able 
to maintain a certain air of primitiveness. Associations of she- 
oaks, 4 black boys, 5 bauksias, 0 seem to afford us glimpses of the 
vegetation which has long since passed away from other portions 
of the earth. (On the other hand it lias to be borne in mind that 
others of our plants — lilies, orchids, compositeae, etc., show the 
same structural development met with in other continents, but 
these are annuals or have no aerial portions during the dry season. 
In fact, although not xerophytcs, their life histories are perfectly 
adapted to their climatic environment.) But, undisturbed by alien 
plant invasion, the local flora has been subject to disturbing attacks 
of quite another nature. The great antiquity of our land has en- 
abled if to experience profound climatic changes. Even north in 
the tropics we find the records of past glacial activity, but the 
change which has done most to determine the present type of our 
flora has been a prolonged period of slow desiccation. Physio- 
graphical evidence indicates that the major portion of our wheat 
belts, now* dependent for summer water on artificial storage of 
the winter rains, once formed portion of the well watered valleys 
of a huge drainage system, the main river of which was a mighty 
stream, estimated by some to have risen in the Murchison region 
and to have entered the sea at a coast line approximating to our 
present-day south coast. Lt is probable that the old river levels 
assisted largely in the grading of the Great Southern Bailway. 
Apart from this, weakly streams such as the Chapman River have 
a flow of water quite incommensurate with their large rock-cut 
valleys, while other ancient river valleys are shown only by exposure 
of 11 ii viable deposits such as those in the railway cutting near 
M ullalynp. Physiographic evidence also shows that at least on two 
arid perhaps on three occasions, after large land uplifts, drainage 
systems were able to reduce I lie land surface to a peneplain at sea 
level. 
The deduction following these facts is that at some remote 
time, the flora of a large part of Western Australia must have 
been in equilibrium with climatic conditions largely determined 
bv a plentiful water supply. Such mesophytic and hygrophylous 
4. Casiiarina Frasoriana. 5. Xanthorrhcea Preissii or X. Rofiexa. 6. Commonly 
Uanksia Meuziesli. 
