Geological History in Palcvozoic Times. 
63 
CHAPTER VI. 
Conjectures as to Geological History in Palceozoic times. 
Lower Palceozoic formations. Snowy River Porphyries. 
Middle Devonian Rocks. Upper Palceozoic beds. 
Having so far generally described the stratigraphical relations 
and lithological character of the great Palseozoic or primary 
group, which constitutes the rock foundation of Victoria, it may 
be well to venture, as suggestions for discussion, some conjectures 
as to the history and nature of the geological changes which took 
place up to the close of the Upper Palreozoic era. The chain of 
evidence is of a rather broken character, and many of the theories 
advanced may he refuted when further testimony shall have been 
obtained. Certain data are nevertheless available, which, though 
imperfect, consist, as far as they extend, of ascertained facts. 
The reasoning on these facts may lie incorrect, and the theories 
advanced may ultimately prove untenable, hut their consideration 
can do no harm, as the discovery and rectification of mistakes 
form important factors in the progress of scientific knowledge, 
and the advancement by any person of an incorrect theory, based 
on a few facts, may often lead to the acquirement of sounder 
knowledge, by inciting inquiry for rebutting evidence in the shape 
of further facts and more exhaustive reasoning on the part of 
others. 
The general deductions as to the geographical history of this 
country do not differ, except in minor details, from the conclusions 
arrived at as to that of other parts of the world. 
In the first place, we see that our oldest rocks, the Silurian 
strata, must have been deposited in horizontal layers to a thick- 
ness, as generally estimated, of about 30,000 feet. Great as this 
thickness appears, it is no more in proportion to the earth's bulk 
than a thickness of stout paper around a gloho of 16 inches in 
diameter. The general character of the Silurian rocks suggests 
that they were deposited in deep water in such broad depressions 
of the earth’s crust as thon existed. Their component materials 
wero derived from the wearing away by water of still older 
igneous, and perhaps also sedimentary, rocks, all vestiges of which 
in situ have been obliterated. As shown in a previous chapter, it 
is very improbable that the foundation on which they were depo- 
sited consisted of granite such as we now see underlying them, the 
present form of that rock being clearly the result of subsequent 
deep-seated Plutonic action. Assuming as correct the theory that 
the earth was once molteu or red-hot, and that it was only after 
E 2 
