GEOLOGY OF OLYMPIC NATIONAL PARK:
PART Il NOTES ON THE GEOLOGY
Hurricane
Ridge Road: Big Meadow
STOP 9:
View of Mount Olympus and pencil slates Where the
Hurricane Ridge Road cuts the ridge just before the Big Meadow parking
lot, slabs of brown, gray, and black slate gleam in the sun. To the
west on a good day Mount Olympus gleams in the sun as well. (fig. FT
18)

Fig. FT 18.
Mount Olympus viewed from south of Hurricane Ridge.
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The slate
forms from shale subjected to great pressure, and the rock tends to
break into thin splinters. Fractures develop in two ways to form the
splinters (called pencils) during the folding of shale under great pressure
(fig. FT 19, 20). The original shale layer is usually made up of many very
thin beds and tends to break along or between these beds. The intersection
of the closely spaced slate fractures and the original bedding combine
to chop the rock into the splinters. In other places pressures exerted
from different directions provide several sets of fractures, and their
intersection produces splinters.

Fig. FT 19. Formation of pencil structure in slates. |

Fig. FT 20.
Well developed and unusually large pencils in slate (The iceax is about 3 feet long).
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