186 
NATURE 
[DECEMBER 24, 1896 
wet season, and his study of the fauna leads him to the follow- 
ing conclusions. 
(1) That in the dry season, when food is scarce and the sum total 
ofactivities is at its lowest point, the various animals, suchas frogs 
and lizards, are dull-coloured, but that this dull colouration has 
not of necessity (as in the case of Amphibolorus barbatus) any 
definite relation to the environment, though it is often in general 
accord with it. (2) That in the rainy son, 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 colouration has nothing to do either with choice of 
partners (reaching its climax after pairing has taken place) or 
with protective colouration—sometimes even it renders the 
animal more conspicuous. 
Limits of space prevent us from summarising any other points 
of interest from Prof. Spencer's most attractive Narrative. For 
a more detailed notice of the zoological collections and conclu- 
sions, we must refer our readers to the review which appeared 
in these columns last July (vol. liv. p. 241). We must mention, 
however, that the narrative is illustrated by eleven plates 
(splendidly reproduced from photographs) and seven figures in 
the text. Among the objects and views depicted upon the plates 
is a striking natural pillar of sandstone—Chamber Pillar—rising 
solitary among the sandhills ; Ayers’ Rock—a huge dome-shaped 
monolith, brilliant Venetian red in colour, and one of the most 
striking objects in Central Australia ; several wonderful gorges 
among the McDonnell Range and Mount Olga. These pic- 
turesque views add to the interest of a well-written narrative. 
General Geological Features. 
We come now to the part of the Report referring to the 
geological and botanical results of the expedition, and here 
again we think that the valuable work accomplished will be 
best made known by summarising the leading features. The 
first section of the third volume opens with a general outline of 
he physical geography of Central Australia, by Prof. Ralph 
Tate and Mr. J. A. Watt. The subject is dealt with under 
seven heads, viz. mountains, rivers, gorges and gaps, lakes, 
claypans, stony plains, and sandhills. The same authors con- 
tribute a description of the geological features of the portion 
of Central Australia examined by them, embracing the country 
lying between Oodnadatta on the south, and the McDonnell 
Ranges on the north. 
Under headings bearing the names of the geological systems 
to which the different series of rocks are assigned, an account is 
given of the general geological features, the ‘extent, thickness, 
mineralogical composition, petrological characters, and fossili- 
ferous contents of the various rocks. Beginning with the Pre- 
Cambrian system, the conclusions of previous observers as to 
the age of the rocks of the McDonnell Ranges, which exhibit a 
high degree of metamorphism, are summarised. These rocks 
have been described as Archean and Azoic, but the authors 
conclude from the fact that a very strong unconformity separates 
the rocks from the Lower Silurian Group, that they must be 
either Cambrian or Pre-Cambrian, and reasons are given for 
favouring the latter alternative. The evidence obtained points 
to much of the metamorphic group having had an eruptive 
origin, whereas the Cambrian rocks of Australia, so far as at 
present known, are entirely sedimentary. In the region 
examined (from Oodnadatta to the McDonnell Ranges) 
Cambrian rocks are held not to be represented. Almost all the 
strata lying between Mount Burrell Cattle Station on the south, 
and the McDonnell Ranges on the north, are included by the 
avthors in the Ordovician system. 
The superstructure of the lowest levels around Lake Eyre 
have long been known to be argillaceous, and to contain marine 
fossils, as at Mount Margaret, Primrose Springs, and Dalhousie. 
The fauna was at first referred to the Jurassic period, but has in 
late years been recognised as contemporaneous with that of the 
Rolling Downs series, regarded as Upper Cretaceous, of Queens- 
land. It has generally been held that the source of supply of the 
natural artesian wells on the west side of Lake Eyre was 
“derived from tropical rains in Queensland absorbed by Cre- 
taceous outcrops, and that the issue of these waters was 
along the line of junction of the Cretaceous water-bearing 
beds with the Paleeozoic rocks on the west margin of Lake 
Eyre. But the now-ascertained far-northerly extension of 
the Cretaceous rocks; and the replacement of the prevailing 
argillaceous condition by sandy strata towards the northern 
boundary make it probable that the source is, after all, of local 
NO. 1417, VOL. 55 | 
origin. Thus, the Finke River from Henbury to Crown Point 
flows approximately along the junction of the Cretaceous 
arenaceous beds and the impervious Ordovician limestones 3 so 
also do the Goyder and Lilla Creeks, particularly towards their 
sources. Moreover, the Cretaceous beds have in the main a 
slight southerly inclination, It is, therefore, highly probable 
that they do absorb some of the flood-waters of those river- 
channels, and conduct them to considerable depths in the 
depressed area margining Lake Eyre ; whilst in no instance do 
the subterranean waters issue at the surface at a level so high as 
that of their conjectural intake. The phenomenon of extinct 
mound-springs, as at Dalhousie, may be explained by the circum- 
stance of a diminished supply ; in other words, that the level of 
saturation has fallen below the level of discharge as a consequence 
of the desiccation of the climate since Pliocene times. 
A hard flinty quartzite or chalcedonised sandstone, varying up 
to fifty feet in thickness, forms the topmost bed of the Rolling 
Down series, and is referred to as the Desert Sandstone. The 
Rolling Down series is held to be akin to the European Upper 
Cretaceous, and the Desert Sandstone is designated Supra- 
Cretaceous, the palzontological difference between the two 
being very slight. The Desert Sandstone of Central Australia, 
on account of its attachment to the Upper Cretaceous, and by 
the occurrence of marine Mollusca of Cretaceous age (at Lake 
Frome well-sinkings), is regarded as coeval with the Desert 
Sandstone of Queensland, which, by its intercalated marine 
sediments, is proved to be Cretaceous; though separated un- 
conformably from the Rolling Down series (Upper Cretaceous). 
The phytiferous beds, which underlie marine Eocene in Victoria 
and South Australia, and are conformable with them, are con- 
sidered as Pre-Eocene. 
As to the origin of the silicification of the Desert Sandstone, 
in the first place, the obsidian bombs and agates which 
occur on the Desert Sandstone plateaus and their slopes could 
not have been transported there by water, unless in the form of 
ice (an hypothesis incompatible with the coordinate features). 
The origin of the Desert Sandstone breccia was certainly not 
due to fracture of the original bed by failure of support arising 
from denuding action, but might have been caused by a lava- 
flow or the deposition of highly-heated volcanic ashes when 
saturated with water. The obsidian bombs demand volcanic 
action, and agates are not infrequently associated with volcanic 
ejectamenta ; whilst the silicates of the ash-beds or lava under 
chemical action would furnish silicated waters asa source of the 
chalcedonising action on the underlying rock-surfaces. The 
development of agates within the volcanic material was only 
another phase of siliceous precipitation. Of this suppositious 
volcanic formation all that remains are the agates and the 
obsidian bombs. The theory may seem wild, because of the 
widespread silicification, and the absence over its area of any 
traces of actual volcanic outbursts; nevertheless, it is held 
that no other explanation accounting for the several phenomena 
appears admissible. 
Excepting the silt deposits of the present water-ways and the 
widespread sand-plains, the only Tertiary deposits of any 
significance are those which indicate a former water-flow of 
vaster volumes than at present. These signs are chiefly in the 
form of gravels, more or less consolidated, through which the 
present water-channels have cut their way, or in the form of 
terraces margining the valley-plains through which now flow 
relatively diminutive creeks. These facts demonstrate that high 
pluvial conditions once prevailed ; and, in consequence, perennial 
flows in the river-channels of this region were maintained, which, 
discharging into Lake Eyre, and supplemented by an Artesian , 
supply in and around it, produced an inland sea of fresh water, 
inhabited by alligators (Padmnarchus pollens) and turtles, and 
on its marshy margin dwelt Dzfvofodon and its fossil associates. 
Inferentially the date of formation of these gravels and river- 
terraces is coeval with the existence of D7frotodon, whose 
extinction was due to those physical causes which destroyed its 
habitats, and gave Central Australia its present rigorously dry 
climate. The marsupial life of this period, on comparison with 
that which replaced it, indicates a high antiquity in the number 
of extinct genera, and the very high percentage of extinct 
species, i 
Gold in the McDonnell Ranges. 
The highly metamorphic character of the Pre-Cambrian rocks 
of the McDonnell Ranges, their greatly disturbed state, their 
extensive development, and, lastly, the presence of numerous 
