[TYRRELL] THE GOLD OF THE KLONDIKE 31 
The study of the detrital deposits found in these valleys is there- 
fore comparatively easy and simple, as no extraneous influences have 
interfered with the regular and ordinary course of natural events that 
formed them. 
Geology.—The rocks which underlie most of the gold-bearing dis- 
trict consist of altered quartz-porphyries, and porphyrites, probably of 
Pre-Cambrian age, which have been squeezed and altered into chloritic 
and serisitic schists. In most places these are now standing at high 
angles and are striking in various directions. 
Included in these schists, and usually running with their strike, are 
numerous veins and stringers of light coloured quartz. In some of 
these veins free gold has been detected, and it would appear probable 
that most of the gold in the district has been associated with, or has 
been derived from, these quartz veins. 
Both to the north and south of these fissile schistose the rocks are 
highly altered gneisses or hard quartz-mica schists, containing some bands 
of limestone. These gneisses, etc., also carry irregular quartz veins, and 
these veins doubtless also contain a little gold, but they would not ap- 
pear to contain as much gold as the veins in the chloritic and serisitic 
schists previously mentioned. 
Intrusive masses of igneous rocks, such as granite, peridotite, dia- 
base, andesite, etc., occur here and there around the border of the 
chlorite schists, but as far as is at present known, there is no definite 
connection between any of these intrusives and the occurrence of gold- 
bearing veins. 
Overlying all these rocks, except the andesites and their associates, 
Cretaceous or early Tertiary sandstones and conglomerates occur 
to the north and south of the chlorite schists. In some cases they would 
appear to have been somewhat folded and contorted, though not to the 
same extent as the older rocks. 
It has been claimed, apparently on good evidence, that some of 
these conglomerates contain gold, and they may thus be ranked as an- 
cient placer deposits, but gold has never been found in them in paying 
quantities, and consequently they have not been studied as fully as 
the later gravels shortly to be described. 
In all these rocks, but especially in the chloritie and serisitic schists, 
which have been called by Mr. McConnell, of the Geological Survey of 
Canada, the “ Klondike Series,” gold is found in greater or less abun- 
dance in the quartz veins which traverse them. It has also been found 
in the schist in minute quantities apparently not associated with the 
quartz at all. 
