358 NATURE [JANUARY 10, 1907 
THE GEOLOGY OF MINING AREAS in section, others are mere swellings along lines of fissure, 
z Beccent sterese Peds N es aie their thinned-out ends being sometimes traceable for miles. 
ME.. IRs {Gr McCONNELL has contributed to the | Mr. Harger discusses the composition of the breccia that 
Annual Report of the Geological Survey of | fills them, and believes that olivine was not an important 
Canada,”’ vol. xiv., part B (1905, price 25 cents), a well- 
illustrated paper of wide interest on the Klondike gold- 
fields. The general topography and the communications 
with other regions are described, and the full-page land- 
scapes convey an excellent idea of the conditions under 
which mining is carried on. Roads have been developed, 
the White Pass railroad is completed, and it now 
takes less than a week to reach Dawson City from 
Vancouver. In the latitude of only 60° N., the surface- 
stratum is continuously frozen, and unfrozen ground is 
reached at depths of from 60 feet to 200 feet. In summer, 
gravel-beds which are unprotected by moss thaw down to 
a depth of from 6 feet to to feet (p. 9). The gold-bearing 
quartz-veins are included for the most part in the Klondike 
series of Microscopic evidence supports the view 
that these schists are of igneous origin, since a passage 
is traceable from uncrushed granitoid types to maylonitic 
sericite-schist (p. 19). Cainozoic rocks are found folded 
in with the schists in Last Chance Creek, thus proving 
the recency of earth-movement in this area. In the basin 
above Rock Creek these beds contain lignites of Upper 
Eocene age. The low-level gravels of the creeks, which 
are so important to the gold-miner, include bones of the 
mammoth, as well as of many existing northern animals 
(p. 29). The greater part, at least, of the Klondike gold 
is detrital, and is derived from the small but very numerous 
quartz-veins associated with the older schists (p. 61). 
Many of the grains of alluvial gold enclose quartz, and a 
schists. 
few are themselves enclosed in quartz. The decay of the 
rocks must have been enormous to allow of the vast 
accumulation of auriferous gravels. The quartz-veins are 
much younger than the schists in which they lie, but are 
older than the andesites and quartz-porphyries of the dis- 
trict. Lode-mining has so far made little progress, but 
work among the gravels seems still increasing. 
Mr. McConnell has also issued through the Geological 
Survey of Canada a paper on mineral discoveries on 
Windy Arm, Tagish Lake, Yukon (1905), where a new 
mineral district has been opened. The quartz-veins here 
bear a considerable variety of silver ores, ranging from 
highly argentiferous galena to stephanite and pyrargyrite. 
In. the twenty-sixth Boletin del Cuerpo de Ingenieurs 
de Minas del Perti Senor Luis Pfliicker describes the gold- 
bearing deposits of the province of Sandia. All the detrital 
material at the foot of the mountains contains gold, with- 
out regard to the nature of the underlying rock. The 
proximity of a moraine formed by an existing glacier 
makes it probable that the detritus has been brought into 
the field by glacial action. Hydraulic mining is carried 
on, as may be. een in the illustrations to the bulletin. 
Mr. Harold Harger brought together a very instruc- 
tive exhibit of diamond= bearing rocks, and of the minerals 
associated with the diamond ‘in South Africa, during the 
British Association in Johannesburg in 
1905. His paper on the diamond-pipes and fissures of 
South Africa is now published (Trans. Geol. Soc. of South 
Africa, vol. viii., 1906, p. 110), and forms a comprehensive 
and welcome contribution, certain details of which are 
sure to meet with healthy criticism. Many hundreds of 
pipes of the Kimberley type are now known to exist, ‘‘ from 
the central and northern portions of Cape Colony, through- 
out Griqualand West, in parts of Damaraland and 
Rhodesia, also north of the Zambezi, and as far east as 
British East Africa. ...In the Orange River Colony, 
there is hardly a district. between the Wesselton Mine 
near Kimberley, the Drakensberg Range, and the Orange 
River, in which the much-sought- for volcanic breccia has 
not been discovered.’? The diamond- -pipes were opened, in 
all probability, after the outpouring of the amygdaloidal lava 
of the Drakensberg, since fragments resembling this rocl: 
occur in the “ blue ground’’ of the Jagersfontein Mine. 
From this and other evidence (p. 115) Mr. Harger conclude: 
that they are of late Triassic or Jurassic age. The pipes 
occur typically in groups, perhaps twenty or thirty nea~ 
one another, and the large ones seem to contain the truls 
rich material. While some are necks, circular or ova. 
1941, VOL. 75 
meeting of the 
constituent of the original mass. The analyses quoted 
from Vogelfontein and the Schuller Mine (p. 120) certainly 
do not indicate a peridotite-magma, though the rock in the 
Kimberley Mine, on the other hand, yields 32-38 per cent. 
of magnesia. The ‘* diamond- fissures,’ to which special 
attention is invited by the author, contain a hard basic 
rock of a less brecciated and more porphyritic character. 
Mr. Harger believes that the material in the pipes was 
injected by explosive action, accompanied by a certain 
amount of heat, though this was not enough to metamor- 
phose the surrounding rocks distinctly. The breccia, in his 
opinion (p. 122), boiled and churned up its constituents 
in the vent. Thus, in opposition to Prof. Bonney’s view 
(p. 126), he holds that the rounding of such masses as the 
included eclogite boulders is due to attrition in the pipe. 
Certainly no one who has seen the breccia of a diamond- 
pipe, such as that of the Schuller Mine, near Pretoria, 
abutting on its apparently unaltered wall, can associate 
Fic. 1.—Weathered Kantoor Sandstone, Transvaal. 
the rock with the phenomena of ordinary igneous flow. 
Equally distinctive is the evidence of the derivation of the 
mention no other 
green pyroxenes and the garnets, to 
minerals, from some previously consolidated and deep- 
seated mass. Few geologists, we fancy, will now dispute 
the conclusion, first indicated by Prof. Bonney when he 
described the eclogite from Jagersfontein, that the diamond 
itself is a derived mineral in the pipes and fissures, and 
arose (p. 134) from ‘an ultra-basic ‘ carbon-saturated ” 
zone at great depth,’’ through which the ‘* kimberlite ’” 
broke. The diamond becomes thus linked in our minds 
with the primitive masses of inorganic graphite, and, still 
more interestingly, with the nascent carbon dioxide, which 
still streams upward from the unexplored regions of the 
crust. 
In the same number of the Transactions of the Geo- 
logical Society of South Africa (p. 147) direct reference is 
made to these ‘‘ juvenile ’’ emanations by Prof. Beck, of 
Freiberg, in a paper on the relation between ore veins 
and pegmatites. The author’s purpose is to connect the 
pegmatites with the aqueous solutions which remain after 
the consolidation of an igneous mass. The old theory of 
‘““ segregation-veins ’’ is set aside, as has been done by 
