April, 1897. EXPEDITION TO CENTRAL AUSTRALIA. 255 



steppes consist of ridges of Ordovician and Precambrian rocks, with 

 an average elevation of 2,000 feet. The cHmate has rainy seasons 

 alternating with periods of extreme drought ; the former are always 

 short, but the latter may be very long. The gibber plains (from a 

 native Queensland word, meaning " a stone ") are a striking feature 

 of the lower steppes ; they are covered with a layer of purple-brown 

 stones, varying from an inch to perhaps a foot in diameter, smoothed 

 by the constant friction of wind-borne sand grains ; they merge into 

 loamy flats, where the Cretaceous rocks are not capped with sand- 

 stone. 



Professor Spencer is of opinion that the development of thorns, 

 so conspicuous in many of the desert plants, is an adaptation to 

 climatic influences and has very little, if anything, to do with protec- 

 tion against animals. A similar view was, we believe, propounded 

 some years ago on independent evidence by Professor Patrick Geddes. 

 A very striking picture is drawn of the contrast between the appear- 

 ance of the country in the dry and wet seasons, especially in regard 

 to animal life. In the former everything is parched and silent ; dead 

 shells of molluscs, carapaces of Estheria, and footmarks of frogs are 

 the only traces of life. In the latter, the trees have put out a fresh 

 growth of leaves, many kinds of birds have suddenly appeared in 

 flocks ; the croaking of frogs is incessant, whilst crustaceans and 

 water-beetles swim about in the pools. Numerous observations were 

 recorded on the colours of animals, the net result of which is thus 

 summarised by Prof. Spencer: — "(i) That in the dry season when 

 food is scarce and the sum total of activities is at the lowest point, 

 the various animals such as frogs and lizards are dull coloured, but 

 that this dull coloration has not of necessity (as in the case of 

 Amphiholiirus bavhatns) any definite relation to the environment, though 

 it is often in general accord with it. (2) That in the rainy season 

 when food is plentiful and the sum total of the activities is at the 

 highest point, various animals are highly coloured, but that this often 

 brilliant coloration has nothing to do either with choice of partners 

 (reaching its chmax after pairing has taken place) or with protective 

 coloration — sometimes even it renders the animal more conspicuous." 



Regarding the relative advantages of rodents, for example, and 

 marsupials in the struggle for existence, the following observation is of 

 interest. The former take care of themselves at an age when 

 the latter take refuge in the maternal pouch. This not only 

 handicaps the marsupial parent in flight, but has the result that if she 

 be captured her family perishes too, whereas if such a mischance 

 happen to the rodent only one life is sacrificed. 



With observations and discussions such as these. Professor 

 Spencer varies the descriptions of the journeys from one water-hole 

 to another, or over the sandhills in the waterless waste to visit Ayers 

 Rock and Mount Olga, — two remarkable masses standing up from the 

 level plain, of which he gives us vivid and striking pictures with both 



