5)

Dawson in 18771 to designate a series of igneous rocks in the vicinity of
Tatlayoco lake, which he could not with assurance assign to the Cascade
crystalline series, the Cache Creek group, or the Jackass Mountain series.
The name Porphyrite was chosen as much of the rock was classed as porphy-
rite. In 1878 Dawson dealt more definitely with these rocks which he in
that year referred to as the Porphyrite series. He stated that they under-
lay and blended with the sediments of the Jackass Mountain series and
that the two members together constituted the Porphyrite series. He
believed that the series bridges “to some extent the gap ordinarily found
between the Cretaceous and Jurassic”’.?

In 1910 Leach? introduced the term Hazelton group for a series of
voleanic and sedimentary rocks in Telkwa, Bulkley, and Skeena valleys
which he considered to be equivalent in age to the Porphyrite group. No
series known to be older than the Hazelton group occurred in the area
worked by Leach, but a younger series of Cretaceous age called the Skeena
series did occur. The name Hazelton group was, therefore, applied to the
igneous-sedimentary group of rocks underlying the Skeena series. The
name Hazelton group was introduced because although the Porphyrite
group might be of the same age and, therefore, correlative, the name when
applied to the rocks of Hazelton district was misleading as the rocks there
were chiefly sedimentary. Leach believed that the rocks of the Hazelton
group were probably chiefly Jurassic.

In 1925 Dolmage* examined part of the area mapped by Dawson in
1875 and collected fossils that showed that the Porphyrite group at Tat-
layoco lake was at least in part of Jurassic age. He also found apparently
conformable sediments shown by fossils to be of Lower Cretaceous age.

Rocks that are roughly correlative with the Hazelton group and
Porphyrite group occur at many places in western British Columbia and
although in some places the age of the strata can be determined precisely,
nowhere are the exact age limits of the whole series known. There is in
the west-central part of the province a series of rocks, the parts of whick
are in the main conformable, consisting mainly of volcanic rocks and clastic
sediments lying between Paleozoic sediments and the Skeena series, and
for which it is desirable to retain the name Hazelton group. The group
can in many places be divided into parts, but in general very few of the
rocks contain fossils of diagnostic value and, therefore, their age can be
stated in only general terms.

The name Hazelton group was applied by the writer® to rocks of sup-
posed Jurassic age of the Alice Arm district. Names of a more local nature
were introduced by the writer® to designate the formations in part of Alice
Arm district but these local names cannot be applied with their original

1“Report on Exploration in British Columbia”; Geol. Surv., Canada, Rept. of Prog.
1875-1876, p. 250.

2Dawson, G. M.: “Report on Explorations in British Columbia”; Geol. Surv.,
Canada, Rept. of Prog. 1876-1877, p. 58.

3“Skeena River District, B.C.”; Geol. Surv., Canada, Sum. Rept. 1909, pp. 63, 64.

4“Chilco Lake and Vicinity”; Geol. Surv., Canada, Sum. Rept. 1924, pt. A, pp. 59-75.

5 “Reconnaissance between Skeena River and Stewart, B.C.’”; Geol. Surv., Canada,
Sum. Rept. 1923, pt. A, pp. 29-45.
; 6“Upper Kitsault Valley, B.C.”; Geol. Surv., Canada, Sum. Rept. 1921, pt. A, pp.
-21.