Maximum: 1m thick, 2.5 m wide.
Bryozoan-coral bioherms.
Mostly branching bryozoa, encrusting bryozoa, rugose and tabulate corals.

Abstract or ref. 1136:
Several small, previously undescribed bioherms are present in the shallow shelf dolostones of the Manitoulin  Formation (Llandoverian) at the Cabot Head and Wingfield Basin localities in the northernmost portion of the Bruce Peninsula region of southern Ontario (Canada). The bioherms, commonly associated with carbonate tempestites, range from 0.3 to 1.0 m in height and 0.9 to 2.5 m in width and are composed of bafflestones-floatstones and minor bindstones. The chief components of the bioherms are dolomitized lime mud and branching bryozoans. Bioherm building by bryozoans, although common in the ancient record, represents a great divergence from the mostly accessory frame encrusting role of bryozoans in modern environments. Minor skeletal components of the bioherms include
echinoderms, rugose and tabulate corals and brachiopods. Laminar encrusting bryozoans exist in the top 10 cm of one of the bioherms. Some of the bioherms show evidence of water agitation that may be the result of current action induced by storm or tidal processes. This evidence includes offlapping debris and abrupt near-vertical margins aligned approximately perpendicular to depositional slope of the basin. The occurrence of the Manitoulin Formation bryozoan bioherms on the Bruce Peninsula stretches the already known Llandoverian reef complex on Manitoulin Island further to the south. The reason why these bioherms did not reach sizes comparable to large Llandoverian or Wenlockian reefs and did not make the shift to a coral-stromatoporoid community is probably related to a complex interaction of internal and external factors such as community development, bathymetry, clasticity, and salinity. 