Trappean Boclcs. 
25 
This greenstone was once largely used by the aborigines for 
manufacture into stone-tomahawks and other implements. About 
a mile north-east of Mount William, near Lancefield, is the site 
(locally known as the native tomahawk quarries) whence they 
principally obtained the stone. 
Wore a number of samples collected and microscopically ex- 
amined, there is no doubt that a very great variety of mineralogical 
structures aud combinations would be shown to exist in these 
trappean rocks ; and, before adopting conclusions as to their 
relation to the ordinary granites, further careful study will be 
necessary. Two probable solutions of the problem suggest them- 
selves. The first, is that the “trap” rocks of the localities referred 
to are simply portions of the 'granitic mass, and, like it, of Lower 
Plutonic origin, but that from some difference of composition, or 
from having cooled under different conditions, their mineralogical 
structure assumed forms different from those common among the 
ordinary granites. The second, is that they are intruded or irrupted 
masses through, or re-fusions of, the granite subsequent to its first 
cooling, and that they indicate the localities of deep-seated volcanic 
activity during Patoozoic times, in which case they might bo 
classed as Upper Plutonic. 
Illustrative examples of the latter theory are described by Mr. 
A. W. Howitt, iu his work entitled “The Diorites and Granites 
of Swift’s Creek and their Contact Zones, with Notes on the 
Auriferous Deposits.” 
In the work referred to, Mr. Howitt gives an exhaustive 
description of the petrological and mineralogical characteristics of 
the igneous and metamorphic rocks of Swift’s Creek, a tributary 
of the Tambo River, and shows that after “regional” metamor- 
phosis of the Silurian rocks of that locality, aud at the line of passage 
from the metamorphic into the normal Silurian rocks, intrusions of 
granite aud diorite took place, which effected around them a still 
further metamorphism (“contact” metamorphism) of the slates 
and schists. Mr. Howitt draws the conclusion that these intru- 
sions took place after the close of the Silurian, and before com- 
mencement of the Upper Devonian, periods, and were probably 
connected with the volcanic activity of that time. These Newer 
Plutonic rocks will, however, be referred to when describing the 
rocks of the Devonian period. 
On the northern margin of the valley of the Wannon is an 
area occupied by igneous rocks, classed as “trap,” of the true 
position of which, whether Older or Newer Plutonic, intrusive or 
contemporaneous (i.e., the lava flows or injected sheets of their 
period), nothing is known. Their character varies in different 
localities. A few miles eastward from Castertou, a dark dense 
greenstone is exposed ill the bed of McPherson’s Creek. It is 
