366 TRANSACTIONS OF SECTION C. 
place in the long succession of earlier and later forms between which it stands; 
for when the elements of a desert landscape are thus seen to be related to many 
other elements, all systematically disposed in time and place, their observation 
and their description are greatly facilitated. 
The equipment of an explorer of deserts with a good knowledge of the 
theory of desert evolution is therefore, as I see it, about as important as his 
equipment with good horses or camels, if it be desired that he should come 
back from his work with a critical record of what he has seen. 
Professor J. W. Grecory remarked that though Scott and R. L. Stevenson 
used the term desert in its old sense for any uninhabited land, at present the 
word is restricted to lands uninhabited owing to their arid climate. No 
numerical limit of desert can be given; and, as Walther has stated, desert can- 
not be absolutely defined on biological, morphological, or climatic grounds. The 
cause of desert is not only climatic; geological and geographical structure are 
both also influential; countries of permeable or friable rocks, and existing as a 
plateau with an easy drainage to the adjacent lowlands, are easily rendered 
desert. The climatic influence depends more on the complex conditions which 
govern the utilisation of the rain and not on its total amount. Proximity to the 
sea is consistent with the development of desert conditions. 
Desert is often more easily utilised than at first appears possible; since the 
soils often contain such rich accumulations of plant foods that the land is very 
fertile when watered. Australian soils often need the addition of phosphate, 
since they contain less phosphorus than the amount held by some authorities to 
be necessary for profitable cultivation. 
He thought that the only explanation of the low phosphorus content in 
Australian soils and the absence of the usual enrichment of phosphorus in the 
soil as compared with the subsoil is that proposed by Professor Cherry, who 
attributes these facts to the rarity of mammals in Australia. In some cases in 
Australia the poverty of phosphate has been more influential than the aridity 
in developing desert conditions. 
Professor A. Prnck : Deserts are regions of the globe which are not only dry 
but are characterised also by the want of vegetation. Taking such a definition, 
Australia has only very few deserts; most of what is called Australian desert, 
indeed, has scrub, even timber. The surface forms of the deserts are more 
closely controlled by water than by wind. The latter heaps up the dunes, but 
its erosive action is rather insignificant in comparison with waterwork exercised 
after rare local rain-showers. Besides this, the surface of many parts of our 
deserts has been shaped by water before the desert conditions came in. But 
there are deserts which have been deserts for a very long period. There has 
been since the end of the Tertiary period a repeated shifting of the climatic 
belts of the earth, which can be observed especially at the equatorial and polar 
border of the desert belts, but from the central parts the belt was not shifted 
away. 
Mr. Grirrira Taytor: The arid region which I know best is situated in 
78° South latitude, but I propose also to discuss the central arid region in 
Australia. 
In Antarctica are many features which closely resemble those described from 
the desert. Angular breccias are being formed abundantly along the facets of 
all the glacier valleys in 78° S. Dreikanter are numerous. Striz are almost 
absent over miles and miles of moraine. The difficulty of determining the 
origin of such deposits in fossil condition is obvious. 
Professor Gregory has always taken an optimistic view of our own arid 
region, perhaps I am less sanguine. It behoves us thoroughly to realise the great- 
ness of the problem seeing that approximately one million square miles has less 
than 10 inches of rainfall. Our visitors who have just seen the region in Western 
Australia have only penetrated the southern fringe. Moreover, 10 inches of rain 
in the south mean infinitely more than in the north where evaporation is so 
great. 
I hope to see a physiographic survey along the 10-inch isohyet initiated, to 
