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20 shows the anticlinal nature of the seam, and Figure 22 some of the small faults seen in No. 1 opening. At the end of the adit at No. 1 opening the seam is cut off by a north-south fault, and in No. 2 opening the seam is also cut off by a fault virtually on the strike, of which the details are not completely worked out.

An interesting case of the swelling and local minor folding of a coal seam due to exposure to weathering agents is seen in No. 3 opening, shown in Figure 20. Most of the thickening and contor- tion of the lenses of white clay and of the seam as a whole appears to be due to the expansion of the seam caused by the action of surface water.

Extent of the Coal-Bearing Horizon.

From the data obtained by boring at Camp Wilson it is known that the coal seam occurs about 400 feet above the base of the Haida formation at that point. The horizon of the seam, that is, the stratum at which the seam would occur if present, must, therefore, underlie a considerable area in the Yakoun basin as indicated on the accompanying map. That the seam is absent in at least part of this area, however, may be indicated by the failure to find coal in the boring put down near the eastern edge of section 36, township 9; although it is probable that this hole was started below the horizon of the coal seam. It is evi- dent that until the area indicated on the map is thoroughly pros- pected, it will be impossible to say that the seam does not occur in any given part; but the possibility of its absence over perhaps most of the district should be kept in mind.

That the seam itself is irregular in its thickness is strongly hinted at by the known irregularity of the enclosing sediments and their poorly sorted character, also by the absence of the seam in the bore-hole noted above. To determine the extent to which this irregularity affects the value of the coal, recourse must be had to carefully made borings.

The uneven nature of the seam recalls those of the Nanaimo!

1Clapp, C. H., Geol. Surv., Can., Mem. 51, p. 106.