Friday, 3 July 2020

HORNBY ISLAND FOSSILS

The beautiful ammonite you see here nestled amongst the seaweed and modern oysters clinging to the grey shales of the Northumberland Formation is the late Cretaceous ammonite Pachydiscus suchiaensis. This is one of my favourite species and is treasured both for its beauty and the fossil site it hails from. 

This darling was found in situ in the 72 million-year-old sediments at Collishaw Point on the northwest side of Hornby Island, southwestern British Columbia.

Hornby is a glorious place to collect. The island is beautiful in its own right and the fossils from here often keep some of their original shell or nacre which makes them quite fetching. This fellow is found amongst gastropods, shark teeth, fossil crabs, baculites and other bivalve fossils. Many of the fossils found at this locality are found in concretions rolled smooth by time and tide. The concretions you find on the beach are generally round or oval in shape and are made up of hard, compacted sedimentary rock. If you are lucky, when you split them you see a fossil hidden within. 

The main topographic feature on Hornby Island is an arcuate mountain consisting of the resistant cliff-forming Geoffrey formation. Near Shingle Spit about half a mile from the coast is Mt. Geoffrey 920-foot peak; from there the mountain gradually drops in elevation to the southeast and to the north.  It consists of a structurally simple 700-foot conglomerate homocline striking N 20° W and dipping to the northeast at a shallow angle of about 6°. The apex of the arcuate mountain belt points to the southwest. The coast of Hornby is probably a rising shoreline, as indicated by the almost perpendicular cliffs along its periphery. A hundred (100) foot cliffs of Lambert shale extends from Shingle Spit to Phipps Point, while from the latter to Boulder Point, the cliffs are not as steep and are covered in many places by vegetation.

Behind the mountain and almost enclosed by it is the fertile, green Strachan Valley. On the large peninsula which extends in a southeast direction from the north of the island towards St. John’s Point, the Hornby Formation outcrops forming the cliffs on the east side of Tribune Bay. The highest of these is about 200 feet. The argillaceous Lambert and Spray formations form the subdued lowlands of the island.