NATirfiAi W .)KF > iM < wni 
viz., (a) the differentiation of silicate magmas into various rock 
types, and (b) the nature and order in which minerals crystallise 
when the molten magma has congealed into solid rock. 
THE XT'LE-UnXE FUIIMATION . 
Resting with a violent unconformity upon these older rocks, 
which SO far as may be judged, formed a broad continental mass, 
or at any rate, a group of more or less closely related islands or 
archipelago, is a great thickness of sedimentary rocks, which has 
been designated the Nullagine Formation. 
This formation is made up in very large part of material 
derived from the denudation of the earlier continental land sur- 
face. It is impossible in the present condition of our knowledge 
to determine the exact amount of erosion to which this land surface 
has been subject prior to Nullagine time. This must have been 
enormous and the delmis from it doubtless formed that great thick- 
ness of sediments, ranging from the' Cambrian to the most Recent, 
which go to make up the beds forming the relatively narrow belt 
in the maritime districts of the State. 
The Nullagine Formation is perhaps the most widely sj)read 
of any of the rock systems exposed in Western Australia, and in 
some respects one of the most imj)ortant. formation has 
been followed from the Oakover River, across the upper reaches 
of the Nullagine. the Coongan and the Shaw Rivers, and from 
thence without a break to Roebourne and southwards to the For- 
tescue River. The same series of constitutes the Hamersley Range, 
which contains Mount Hruce, one of, if not actually the highest 
summit of the State, it also makes up that rough taldeland which 
divides the waters of the Lyons from those of the Ashburton 
River. The southernmost boundary of this large exposure is in 
the neighl,)Ourhood of Mount Russel, in south latitude i^Odeg. dOlat., 
not far to the south of Lake Way. In its lithological characters, 
its behaviour and general aspect, the Nullagine Formation bears a 
very striking resemblance to those beds which constitute one con- 
tinuous series in that tableland, which extends from W'yndham to 
Mount Hart, a prominent summit near the southern face of the 
King Leo]K:)ld Plateau, in the Kimberley Division. 
The Nullagine l’'ormation makes a very i)rominent feature in 
the landscape in those regions in which it is developed, presenting 
as it does a plateau-like appearance, owing to certain of the harder 
l)cds standing out in hold relief, and forming mural faces at differ- 
ent levels as at Mount Margaret in West Pilbara. (Fig. 11). 
Lithologically the strata consist of a group of sedimentary 
rocks, sanrlstones. quartzites, conglomerates, and dolomitic lime- 
stones. Associated with these beds, igneous rocks are specially 
abundant, and according to their mode of origin they are readily 
divisible into two classes, some were formed from congealed molten 
