64 
Geology and Physical Geography: 
it had sufficiently cooled that water could rest upon its surface, it 
is easy to conceive that there would be a vast quantity of loose 
incoherent material, volcanic dust, ash, &c., which would at once 
be taken up and temporarily held in suspension by the water when 
the latter first settled on the earth. Add to this the heated con- 
dition of that water the natural chemical and mechanical operations 
which must have ensued* and the length of time they continued in 
action, and the formation of so (comparatively) thill a layer — 
resulting from the re-distribution of pre-existing matter — as the 
total thickness of all the sedimentary Palaeozoic formations of 
the earth’s present crust would amount to, is easily accounted 
• for. 
Recent researches have shown that in deep seas, even at the 
present day, there are frequently vast “mud clouds,” the deposit 
of which on the bottom is exceedingly slow, and it may well be 
imagined that the water which first enveloped this earth may have 
for a time been able to hold in suspension the materials of all the 
sedimentary rocks now visible. The probable greater bulk of the 
earth, and the larger amount of water on its surface, has already 
been alluded to. 
Consequent on the diminution of the earth’s bulk through 
contraction in cooling, the next processes were the folding and 
corrugation of the layers which had been deposited, their meta- 
morphism, and invasion or partial absorption by molten igneous 
matter. 
There is no reason to believe that these movements, as regards 
the Lower Palaeozoic strata, took place simultaneously all over the 
earth, or that they were of a sudden character ; they may, for 
instance, have commenced during the Lower Silurian period, and 
have been in gradual progress during the actual deposit of the 
Upper Silurian rocks. The action of regional metamorphism may 
also be regarded as having taken enormous lapses of time to 
accomplish its elTeets, and so also the consolidation of the molten 
masses into the forms of granite, porphyry, &c., was no doubt the 
work of incalculable ages. Neither was the Plutonic action, of 
which these rocks are the results, confined to one period, for as 
already shown there is evidence of its occurrence at distinct 
intervals. It was from the folding and squeezing together of the 
Lower Palaeozoic rocks that the first rude geographical distribution 
Of land and water surfaces properly resulted. The broader anti- 
clinal and synclinal undulations formed respectively the elevated 
land surfaces and the depressions occupied by the sea. This 
period witnessed the elevation of the general axial line of the 
Australian Cordillera, not as we now see it, in the form of a narrow 
but well-defined and tortuous ridge, but as a broad elevated 
brokeu plateau, having no defined water-shed line, but forming a 
continuous land surface from Tasmania to New Guinea. 
