28 
The Queensland Naturalist 
May, 1942 
as both food and drink. 
Many desert animals adopt the burrowing habit (as 
for instance, the frog just mentioned, and several Aus- 
tralian marsupials) and so escape from the extreme heat 
and aridity of the surface of the desert. One Australian 
creature, the marsupial mole, leads so entirely a subter- 
ranean existence that it has lost the use of its eyes. 
So far we have been speaking of deserts in general 
terms, but it is now necessary to distinguish between dif- 
ferent types of deserts. At the beginning of this address 
it was pointed out that aridity may be due to heat and 
physical drought, or it may be due to the more or less 
permanent frozen state of the soil. The former are often 
referred to as ‘‘Hot Deserts” and the latter as “Cold 
Deserts.” Hot deserts occur in all continents near the 
Tropics of Capricorn and Cancer, usually inland, but 
extending to the coast in some places, as in North-west 
Australia along the 90-mile Beach, South-west Africa, and 
Chile. There are three very distinct types of Hot Desert, 
though more than one may occupy the same region. These 
distinctions are based on the nature of the surface of the 
ground, which may be composed of sand, rock or rock- 
fragments, salts, or other substances. In the first of these, 
the Sandy Deserts, the ground-surface is composed of long 
parallel sandhills or “dunes” as they are often called, 
alternating usually with narrow, hard flat expanses called 
“claypans.” The claypans may be almost perfectly 
smooth, or some stone fragments may occur. In its char- 
acteristic development in the Arunta or Simpson Desert 
of South Australia, Northern Territory, and Far South- 
west Queensland, the dunes’ follow the direction of the pre- 
vailing wind (approximately N.N.W. in Queensland), are 
on the average 40-50 feet high though more rarely up to 
60 feet, and may run unbroken for 20 miles or more. The 
crests are from one-quarter to one-sixth of a mile apart. 
In Western Australia the dunes may be as much as 100 
feet high, but most of the reports of dunes as high or 
higher are rough calculations of travellers who have based 
their estimations on the difficulty experienced in crossing 
them — a natural error readily pardoned by anyone who 
has had to traverse these dunes. In some parts of the 
world the dunes lie transversely to the pravailing wind. 
Occasionally the land surface may .be nearly level or with 
