68

More detailed descriptions of these rocks will be found in
Chapter V.

Structure.—Internal. The widths of the dykes vary from
a fraction of an inch to 50 feet or more. Sills up to 200 feet
thick have been met with, but they are exceptional, and may be

Geological Survey, Canada.

Figure 6. Vertical section of andesite sill on north side of Triangle island,
Skidegate inlet, cutting shaly sandstones. Illustrates chilled
contacts, and upward translation of vesicles. Sill is 3 feet 6
inches thick.

laccoliths. The average width of the dykes, excluding two of
30 and 50 feet respectively, is about 5 feet. There is little
variation in the internal structure of the injected bodies. Many
ee show chilled contacts in varying degrees, but it is not uncom-
mon to find the grain uniform throughout. Some of the bodies