636 
By far the greater part of the stream tin is in fine grains of the size of a pin’s 
head and under, and almost always reveals under the lens some trace of an original 
crystalline condition. It contains a large proportion of the “ruby” and “amber” 
varieties. Together with quartz granules, it forms, as a general rule, the matrix of a 
coarse, imperfectly cemented conglomerate or gravel of quartz and granite pebbles. The 
pebbles are often rather squared than rounded. They are not of a nature to retain 
stiiations well, but the shape of some of them leads me strongly to suspect that their 
attrition might, in the first instance, have been due to glacial action. The crystalline 
fragments of fel.-'par, which have frequently been carried into the wash along with the 
quartz and tin-stone, have in most cases decomposed into a stiff kaolin, which sometimes 
helps to keep the wash together. 
The tin wash is for the most part confined to the layer of gravel or uncon- 
solidated conglomerate lying directly on the bed-rock. This gravel is generally 
overlaid by a varying thickness (up to twenty-five feet or more) of gritty sand, which 
is occasionally interrupted by thin layers of gravel (with streaks of tin-stone) or of 
clay. 
After an examination of the alluvial workings (in 1882), I concluded that the 
tin-stone, in its original matrix, must have been in the form of crystals, rarely of large 
size. The ore was probably eoncentvated by the weathering of its matrix — whether reef, 
lode, or dyke and of the encasing granite country during a long period of gentle 
subaerial denudation, when the rains were never sufficiently heavy to remove the tin, or 
even the larger quartz stones, from the hillsides where they were left by the decay of 
theii matrix. To this there apparently succeeded a limited period of heavy rainfall, or 
possibly of snow whose melting produced a rush of water sufficiently strong to “sluice” 
the general surface of the hill country, and to deposit its heavier materials (including 
the tin-stone) in the upper reaches of the Severn and its tributaries, while carrying off 
its finer particles to the plains of the south-west. To the now current period belong 
the accumulation, under temperate conditions, of the existing surface-wash on the hill- 
sides (moderately rich in tin ore), and the deposition of the sand (almost destitute of 
tin ore) which overlies the tin wash in the streams. 
Two distinct types of tin-bearing rocks are met with in the district— quartz reefs 
and igneous dykes. 
The reefs are best developed in the ridges on the left bank of Quartpot Creek, 
nearly opposite Sommerville’s Homestead. Here are the outcrops of at least seven reefs 
or veins, four of which bear north-north-east, one north-east, and one east and west. 
These reefs are of highly crystalline quartz (sometimes smoky), and all contain much 
wolfram and moderate-sized crystals of tin ore, the latter almost always confined to 
faces a.nd joints. Such reefs are apparently the sources of some of the coarser stream 
tin which is locally met with. 
The dykes are composed of granular quartz, fine scaly lithia-mica, and small 
crystals of tin-stone, and form a rock much resembling the stanniferous greisen of 
Saxony. They seem to have been erupted in a molten condition (bringing up the tin oxide 
with them) among fissures in the granite. The tin-stone bears, in some samples I have 
seen, a proportion of five or ten per cent, to the general mass of the rock. Dykes of 
this character are seen at various points in the Eange on the Boundary of the Colony 
between the heads of Kettle Swamp and Sugarloaf Creek. They run at varying angles 
from north-north-east to east-north-east, coinciding in their direction with a system 
of jointing which characterises the granite. The tin-ore crystals of the dykes are 
precisely what, with a little attrition, would form the main mass of the stream tin of the 
heads of the Severn. 
