66 
Geology and Physical Geography: 
channels in the Silurian and granitic rocks. The general principle 
may here be stated, that in past geological times as now, wherever 
a land surface rose above the sea, the action of denudation was 
constantly removing material from such surface to the sea, where, 
according to circumstances, it was re-distributed in fresh forms. 
Briefly stated, emergence above the sea implies loss ; submergence, 
accumulation. The close of the Lower Devonian period appears 
to have been marked by a general submergence of the land surface, 
naturally accompanied by encroaching littoral denudation, and the 
erosion of bays and inlets, but without immediate cessation of the 
volcanic activity which had been at work for so long, as evidenced 
by the igneous character of the earlier aqueously-arranged Middle 
Devonian beds of Buchan. Finally, the volcanic fires appear to 
have become extinct, aud the land to have been depressed to a 
great depth beneath the ocean, in the bed of which the limestone 
deposits then accumulated in the deeper hollows in the older rocks • 
aud while the limestones were in progress in some places, beds of 
a different character — the shales, slates, quartzites, &c„ of Tabber- 
abbera — were being laid down in another. Further contraction of 
the earth’s bulk and other influences caused the uplifting, folding, 
compression, and partial metamorphism of these new layers, 
whose basset edges were, in their turn, subjected to abrasion, and 
partly denuded simultaneously with the still further denudation 
of the Silurian rocks. These Middle Devonian formations have 
only been identified in the eastern portion of the colony, and in the 
central portions, or on the southern and eastern slopes of the great 
Lower Faheozoic mass. Any rocks of this age that may have 
been deposited on the western, north-western, and south-western 
slopes have been totally removed by denudation, or, if any vestiges 
do remain, they arc concealed by newer formations. 
The striking strati graphical unconformity between the Middle 
and Upper Devonian rocks has been already noticed ; the former 
are sometimes nearly vertical, while the latter are, in many places 
seen to rest almost horizontally on their upturned edges. This 
seems to indicate an emergence of the land, and a long continuance 
of terrestrial aud littoral denuding action on the Middle Devonian 
and older rocks, subsequent to their plication and partial metamor- 
phism, and prior to the commencement of the beds of the Upper 
Palaeozoic group, in which are included the Upper Devonian rocks. 
It has been shown bow the rocks of the Upper Palaeozoic divi- 
sion are most extensively developed in two great groups — one that 
of the Grampian sandstones in the western portion of the colony, 
and the other comprising the belt extending from Iguana Creek 
to Mansfield, in the central eastern district. In his work, pub- 
lished in 1866, Mr. A. R. C. Selwyn indicates the probability that 
these two masses are respectively the western and eastern rem- 
nants of a great anticlinal arch of Upper Palaeozoic rocks which 
