The Hamill Group, of presumed early Cambrian age, is discussed with respect to its correlation, its lithology, provenance and deposition.

This group, located on the west side of the Rocky Mountain Trench, is correlated with the Gog Group of the Rockies on the east side of the Trench. In the Lake Louise area, Walcott (1910) proposed a threefold subdivision--th topmost St. Piran Formation, the middle Lake Louise Formation and the lowermost Fort Mountain Formation. Such a threefold partition has been found useful in the southern part of the Dogtooth Mountains by Evans (1933) and also by the present writer. In addition, the present author has measured a section, at Timber Mountain, where no such subdivision is possible.

In all, six sections are described and measured. Point counts of 104 thin-sections confirm field observations of a restricted mineralogy. The typical Hamill quartzite and argillite have the following composition, stated in per cent of points counted in thin sections:

                                                     Quartzite  Argillite
Quartz                                                   69        38
Sericite (and clay-like particles)                       18        40
Carbonate (as calcite, dolomite)                          2         4
Iron (as siderite, limonite, hematite, magnetite)         3         5
Muscovite                                                 3         6
Chlorite                                                trace       4
Feldspar                                                  4         2
Miscellaneous (inclusions, coating on grains)             1         1

Iron compounds of several varieties are the principal coloring agents.

Ninety-seven crossbeds were measured and corrected to original orientation. The resulting rose diagram indicates a current direction from the northeast.

The writer is of the opinion that the quartzite phases of the Hamill Formation have as their paleosource a granitic area to the northeast, probably the deeply eroded surface exposed after the Hudsonian orogeny of 1800 million years ago. The detritus of the Lake Louise--and other argillite interbeds--may have originated on the landmass of Montania to the south of the map area.

The top of the Hamill is transitionally conformable with the overlying Donald carbonates. The basal contact with the Precambrian Horsethief Creek units is conformable within the area discussed.

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