58 T. W. E. DAVID. 
It would be most useful, if engineers and others, would keep 
accurate records of any sections obtained in borings or excavations 
in these alluvials, especially in cases where they descend below 
sea level. 
(2) Eruptive rocks. These may for convenience be divided 
into (A), a Pre-Triassic Group older therefore than the Blue 
Mountains, and (B) a Post-Triassic Group of later origin than the 
formations of the Blue Mountains. 
(A) Pre-Triassic—(i.) Granites. These rocks are represented 
chiefly by granites, which are seen outcropping to the west of the 
Megalong Peninsula, near Katoomba, and which extend thence 
into the valley of Cox’s River, and occupy considerable areas near 
Hartley, Rydal, etc. They are biotite granites, rendered porphy- 
ritic in places by orthoclase felspar. These granites are probably 
of the same age as those of Bathurst, which have already been 
described by the Rev. J. Milne Curran. At the latter locality 
they are rich in sphene. As already mentioned these granites 
near Rydal have intruded the Lepidodendron beds, but no 
evidence has as yet been adduced to show that they intrude the 
Permo-Carboniferous rocks in the Blue Mountain region. On 
the other hand, near Hartley and Marangaroo, granite pebbles 
may be noticed in the basal beds of the Permo-Carboniferous 
System. (See Plate 2.) 
(ii.) Diabasic Lavas. Sheets of eruptive rock, apparently of 
contemporaneous origin with the Upper Marine Series, are seen 
in the railway cuttings between Rylestone and Lue, especially 
near the Rawdon Coal Mine. They may have been erupted 
contemporaneously with the great series of andesitic dolerites and 
tuffs of the same geological age at Kiama. 
(iii.) Tuffs of a basic character, and dipping at a steep angle, 
occur high up on the western escarpment of the Blue Mountains, 
at Cumberamelon, on a horizon about midway between the Lithgow 
Coal-seam and the seam at the top of the Permo-Carboniferous 
Coal-measures. They somewhat resemble the tuffaceous beds 
