Landforms of British Columbia 1976 - Department of Geography

pendants which, because of their sedimentary laminations, tend to produce an
oriented topography.
Some intrusions have a primary gneissic structure, which is the result of parallel
orientation of minerals, and which may be stmiciently pronounced to influence the
topography. A common feature of large batholiths, and one well illustrated in the
Coast Intrusions, is the presence on a regional scale of well-developed joints. These
fractures are sticiently prominent to influence the orientation of valleys and ridges
and to give a pronounced rectilinear pattern to the topography (see Plates VIA
and XLVIII) .
Figure 2. Diagram showing the main areas of intrusive igneous rock.
Areas of dominantly intrusive rocks are shown in Figure 2. Such rocks occupy
a very large area in the Coast Mountains, and their presence explains similarities in
topography that extend over a length of almost 1,000 miles. Intrusive rocks are
extensively exposed in the Cassiar-Omineca Mountains, across the southern part of
the Province, and in the southern part of the Columbia Mountains. Smaller areas
of intrusive rock are scattered throughout the interior of British Columbia from the
International Boundary to the Yukon Border, and on Vancouver Island and the
Queen Charlotte Islands.
Intrusive rocks, wherever they occur and despite. local peculiarities of erosion,
impart a characteristic appearance to the landforms developed on them.
(2) Sedimentary rocks consist of successions of similar or diverse beds. In
general, they consist of layers a few feet, or possibly tens or even hundreds of feet,
thick, with physical characteristics that may persist for many miles. When the sedimentary
beds are flat lying or only very gently dipping, the topography has a dis-
16