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look like candy canes, others are shaped like snails. Some are completely un-
coiled, others only slightly so. This rich diversity proclaims that ammonites,
even this late in theit history, wete wildly successful creatures. During the
time that the Haslam Formation was being deposited across much of the
Vancouver Island region, they proliferated.
The presence of ammonites in the Haslam Formation is a sure sign that
these tocks were formed in the sea, not on land. The ammonites tell us that
the Haslam Formation can be approximately correlated to rocks in the West-
ern Intetior that contain ammonites and ash beds. Those ash beds are radio-
metrically dated at over 80 million years in age. This figure gives us a sense
of the maximal age of these sediments on Vancouver Island.
The Haslam Formation can be seen in river cuts and shorelines, and it
is usually tilted as a result of regional land movement and mountain build-
ing. As on Sucia, when the formation is tilted, we can most easily measute
its thickness and most easily observe the rocks that succeed it. Any package
of sedimentary rock was originally like a layer cake, and the Haslam Forma-
tion is like a deep, dark chocolate layer close to the bottom of our cake. It is
overlain by rocks very different in appearance.
Near the top of the Haslam shale a curious thing happens. The rocks
begin to change grain size. The fine mudstone and shale gradually change to
sandstone which is then abruptly overlain by an enormous thickness of con-
glomerate that looks somewhat like the conglomerate on Sucia but is usually
composed of larger cobbles. The transition is dramatic. For whatevet reason,
the environment where, for more than 1 million years (and perhaps as long
as 5 million years) only fine mud particles accumulated on the bottom of the
sea suddenly began to receive gravel, pebbles, and larger hunks of rock. This
transition clearly records a dramatic change in the environmental history of
the region. It also marks a change in formations. The top of the Haslam For-
mation is marked by the last marine shale. In many cliff faces and river cuts,
we can observe the rocks that succeed the shale; they are composed of very
prominent conglomerates. This lithological transition defines the boundary
between the fotmations.
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