70

Some of the dykes show a similar structure, and particular
cases are illustrated in Figures 8 and 9. In the case of Figure
9 there seems to have been an excess of magma at the point
illustrated and the overflow forced its way irregularly into the
sandstone.

Geological Survey, Canada.

Figure 7. Plan of 4-foot andesite sill on east end of Lina island, Skidegate
inlet, illustrating intrusion en echelon, baking of sediments, and
later, finer grained andesite dyke.

That some at least of the dykes and sills were injected before
deformation ceased is shown by the tightly folded sills occurring
in the tunnel of the British Pacific Coal Company, and by the
folded and faulted dyke in the tunnel at Camp Robertson,
Figure 12.

Method of Intrusion. It will later be shown (page 113) that
the dykes occupy almost exclusively fissures belonging to one
of four systems of joints. The joints of this system, therefore,

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