The formation was produced at the time when ammonites, gryphites, oysters, Pecten, Mytilus, etc., etc., lived.
"More Letters of Charles Darwin" by Charles Darwin
Mytilus, as fossil in the Andes.
"More Letters of Charles Darwin Volume II" by Charles Darwin
Genres Pinna, Mytilus, Modiola, Nucula.
"Lamarck, the Founder of Evolution" by Alpheus Spring Packard
On the rocks we found a patella and a small chama, but we saw no mytilus.
"Narrative of the surveying voyages of His Majesty's ships Adventure and Beagle, between the years 1826 and 1836" by Robert FitzRoy