84 
On the North-West coast there are several trap dykes, whilst South of the i 
Nullagine, and on the Fortescue River, there are several lava flows, as well as 
dykes. The largest development, however, is met with in the Kimberley district, | 
where an extension flow stretches from the head and East side of the Ord River | 
into the Northern Territory of South Australia. Obsidian bombs are found all j 
over the interior, but where they come from no one knows. 
Plutonic. 
These rocks occur throughout the Colony amongst the crystalline rocks, which j 
they have displaced and metamorphosed. The granites are seen most abundantly I 
in a belt of country about 50 to 100 miles wide, running North and South about 
150 to 200 miles inland, where, rising out of the alluvial plains, they form bold 
red isolated hills. 
Trap rocks, usually dioritc, are found all over the Colony; their caps often | 
split up, and weather into rounded masses having a waterworn appearance, owing j 
to the corners being first disintegrated, then exfoliated, which eventually causes the 
formation of rounded boulders. 
Amygaloids are met with in great variety in the North-West, where they form 
huge rugged hill masses, upon which it seems nothing will grow. Both the matrix 
and the enclosures vary much in different places ; the latter are most commonly 
agates and calcite. 
MINERALOGY. 
With a Description of the Minerals of Commercial Value which have been or are 
likely to be found in this Colony. 
A Mineral is a substance obtained from the earth’s crust by digging or 
mining. It may have been originally of organic origin, which has undergone 
certain changes called mineralisation, principally caused by heat, mineral water, 
and pressure. Coal is a mineral of this class, but the larger number of minerals 
are not of organic origin. 
Mineralogy is the study of the physical properties of minerals, such as their 
chemical composition, crystalline form, hardness, specific, gravity, colour, etc. 
As in the study of mineralogy a knowledge of chemistry is necessary, a list of 
the elements, with their symbols and combining weights, is given here. 
List of the Elements, with their symbols and atomic weights: — 
Aluminum 
Al. 
... 27-0 
Antimony (Stibium) ... 
Sb. 
... 1220 
Arsenic 
As. 
... 74-9 
Barium 
Ba. 
... 136-8 
Beryllium 
Be. 
9-0 
Bismuth 
Bi. 
... 2100 
Boron ... 
B. 
11-0 
Bromine 
Br. 
79-8 
Cadmium 
Cd. 
... 111-7 
Caesium 
Cs. 
... 1330 
Calcium 
Ca. 
39-9 
Carbon . 
... c. 
... 12-0 
