4 
felspar, triclinic in small quantities. Until more carefully examined the rock at Port Darwin camp may be 
called 44 diorite. ,, There are also diorite dykes in many places, especially where the gold has been abundant, 
such as at Margaret creek and other places. In addition, the country is interlaced in abundance with dykes 
or veins of a greyish-blue flaggy roca. of volcanic character and extraordinary hardness. 
These dykes are narrow aud of great length—sometimes several miles. Throughout their course they 
stand out like flagstones, often 10ft. above the ground. The stone is fine grained, and not vesicular. It 
resembles phonolite, but I must defer any decision as to its character until I have had sections examined. 
What are the relations of these dykes to the auriferous rocks is hard to say, but they always accompany 
them. That diorite dykes are accompanied with singularly rich shoots of gold, is what experience through¬ 
out the colonies has borne out. These dykes of phonolite (?) appear to be more modern. There arc many 
instances where they accompany a white barren quartz. Probably they are not connected with gold in 
one way or the other. The quartz veins generally, though not always, run along the summits of the ranges, 
as their existence has preserved the ridge from decay. This gives rise to a peculiar aspect to the hills, which 
are a series of sharp ridges, with saddles between. Of course the quartz lodes run parallel with the hills, as 
they are in fact the nucleus of the ranges. 
The strata around the reefs are frequently metamorphosed for a short distance. At the Eleanor mine, 
Pine creek, the casing is crystalline with crystals of staurolite. At the McKinlay mine the walls arc pink 
granite and much mica. At Springhill mine the ground is faulted in successive steps as it were. At the 
Eleanor reef the country is mixed up, crushed, and faulted, in much confusion, yet not sufficient to prevent 
the lodes being followed. The lodes or quartz reefs vary in their mineral contents. For the most part they 
are gold veins of the usual character, but they are also mineral lodes of silver, copper, lead, tin, and probably 
nickel, graphite, iron, and manganese. I have seen no antimony. 
The term generally used by the miners for the outcrops of the heads of a vein is a “ blow,” and the idea 
of their origin is connected with the action of fire. Whatever may he the origin of veins, it is certain that 
the burnt red and black appearance is the result of exposure to the action of air and water, which has rusted 
the iron ores and decomposed the other minerals. For a long time past the miners have had a prejudice 
against what are called 44 iron stone blows,” or caps of lodes in which there was a great development of per 
oxides of iron. They have often been tried and found poor in gold, or destitute of it, so that even prospecting 
them has been generally abandoned. There are a good many throughout the district, and the majority have 
been untouched. They are the heads of true mineral lodes, the mineral character of which will not he deter¬ 
mined until the water-level is reached. Silver, copper, and lead are the principal minerals to be expected in 
them, with, probably, a little gold. I think they are rich ores, but not suited for ordinary methods of treat¬ 
ment, or the battery appliances in use here. New and patent methods for the separation of the ores will 
have to he adopted. Flic experience of the Ravcnswood (Queensland) miners will be found of service in the 
Northern Territory. There is in most respects a close similarity between the two mining districts. 
Granite .—The peculiarities of the metals will be dealt with presently. The rest of the geology of the 
country may he dismissed in a few paragraphs. All round the mining area there is a belt of granite. I 
infer that it is a complete ring, though I have not traced it in every part. Thus, granite is found on the west 
side all along the telegraph line, and on the east side all along the valley of the Mary, on the north side from 
the Fergusson to within four miles of Pine creek, and on the south about the neighborhood of the Finniss 
river. On the north-west aud south sides of this belt the granite is pink in color, coarse grained with large 
crystals of orthoclase felspar often two inches and more in length. Usually this coarse kind of granite is 
termed granite porphyry. On the west side it is partly of this kind, but on the east its place is almost 
entirely taken by blue, close grained granite—a valuable stone. On all sides this granite crops up into 
hills of 100ft. and more in height, hut never quite so high as the metalliferous slates. 
I he existence of this belt of granite round the mineral deposits is of the greatest importance. It is a 
state of things which all experience has taught to be the most favorable for mineral deposits. Usually tlie 
greatest richness is found at the edges of these formations, or rather at the junction of the slates with the 
eruptive granite, and from what I have seen this locality seems to be no exception. All along tlie east side 
of the ranges, or the valley of the Mary river, there is a continuous outcrop of mineral veins almost upon the 
junction. The Eveleen Silver mine is actually upon the extreme edge of the latter, hut the section is not 
visible, as it is overlaid by a small outlier of ancient limestone. This is one instance, but there are many 
more which have never been prospected to the north and south along the valley of the Mary. 
It would seem as if silver, lead, copper, and tin were the metals developed on the edges of this junction, 
while gold exists generally throughout the slates. But the district is hardly sufficiently prospected to form 
safe conclusions. The width of this ring of granite varies as far as it is known. On the south of Pine 
creek it is at least fifteen miles wide, and in some parts of the valley of the Mary it must be nearly as much, 
as well as on the north. On the west it is overlaid by sandstone and magnesite rocks. An accurate 
geological survey of this line of junction would lead to the discovery of many mineral lodes. 
As far as 1 have seen the minerals are found in the slate country only. There are quartz lodes and 
other lodes in the granite, hut they have proved barren as yet. Not that gold and other minerals may not 
be found in granite, as they are in Charters Towers and in Victoria, but there are few exceptions to the 
following rule: Where mineral veins pass from one formation to another they change their character. 
I hus, if they have been rich in slate country and pass into granite, they will become poor and barren, aud 
vice versa. When the belt of granite is traversed we find that the metalliferous formation again crops out 
on the north and south—thus the whole country between Southport and Port Darwin consists of that 
formation capped here and there with a little magnesite. There are many quartz lodes, and I am of opinion 
that the outcrop of ironstone in ridges of black nodular limonite marks the locality of mineral lodes. There 
is every reason to suppose that the junction between the granite and slates on the outside of the granitic 
ring should be as rich in mineral lodes as the inside line of junction. Mineral lodes, which become barren in 
passing from one country to another, become metalliferous in returning to the country from which they took 
their origin. Thus then the edge of the granite country on the outside of the belt to the westward of the 
telegraph line to the south of the Fergusson aud north of the Finniss should he prospected, and may prove 
to he rich in minerals. 
Limestone .—Next in succession to the granite aud the folded and contorted slate strata comes a small 
outlier of ancient crystalline limestone, which occupies a small area of a few hundred acres at the Eveleen 
mine. 1 lie strata are contorted, and even bent and folded into rude circles. Besides presenting the usual 
weathered appearance of limestone, of fantastic pinnacles, &c., this formation has a most peculiar aspect from 
the 
