The area of southwestern British Columbia holds a thick series of young formations which, known to be entirely Cretaceous on Vancouver Island, have been called Tertiary on the mainland side of the Straits of Georgia. The structural unbalance embodied in this interpretation has long seemed a reason for doubts regarding it.
The well known Cretaceous sections of Vancouver Island are reviewed in the light of the most recent field evidence and revised paleontology. The molluscan faunas provide the exact dating of the formations; the intercalated fossil-leaf floras indicate correlations with formations on the mainland that are without molluscan faunas.
Confirmation of these correlations was obtained by a completely independent method. Microfloral analysis was applied, and ten categories of pollen and spores which occur in this region were treated statistically. The material belongs in three age groups: Campanian, Paleocene, and Eocene.
It is concluded that these deposits of supposedly various ages in different areas are, if the small Eocene deposits are excluded, one extensive series from Upper Cretaceous to Paleocene. It is shown, also, that the profound Cascade Range orogeny which involves all these deposits except the Eocene is of early Cenozoic date.