Abstract

Seashore exposures in the Cow Head area display a succession of limestone conglomerates interbedded with shales and limestones. Conglomerate layers range in thickness from 1 foot to more than 200 feet. The material consists of flat angular chips or moderately rounded boulders of fine-grained gray or white limestone. Fossiliferous boulders from any one layer yield trilobites of the same limited age.

Boulders from the lowest fossiliferous conglomerate at Broom Point contain Kootenia, Zacanthoides, Orriella, Agraulos, and Peronopsis. Succeeding bedded limestone yields Meneviella and Tomagnostus. A boulder in the overlying conglomerate also contained Meneviella and Tomagnostus.

Cambrian conglomerates at Cow Head yield younger trilobites in successive layers: Tricrepicephalus appears in the lower, then Taenicephalus, followed by Ctenopyge, Rasettia, and Keithiella. Above are beds with Staurograptus and Dictyonema, overlain by conglomerates with early Ordovician trilobites.

Successively higher black shales contain graptolites of the Levis Shale zones, and interbedded conglomerates yield successively younger Ordovician trilobites. Shale with Trigonograptus and Isograptus underlies the highest conglomerate which yields Nileus, Bathyurellus, Remopleurides, and Ectenonotus. The thick limestone conglomerate at Lower Head includes enormous boulders, one of which contains many of the trilobites described by Billings (1861–1865) as from Cow Head. This layer is underlain by black shale with Isograptus.

The Cow Head Group, therefore, is not a single formation but a succession of conglomerates and intervening beds ranging in age from Middle Cambrian to Middle Ordovician. With few exceptions the boulders of any conglomerate are approximately the same age as the immediately underlying strata. The limestones of the fossiliferous boulders formed in shallow water; the beds intervening between the conglomerate layers formed in deeper water and consequently are almost devoid of fossils other than graptolites.

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