Platform edge Epiphyton/Renalcis boundstones in upper Shady Dolomite Fm.
Boundstones several m thick forming up to 60 m thick reefal complexes.

Reefs in both Botomian (Austinville Member) and Toyonian (Upper Shady Dolomite Member)

Abstract ref. 1615:
Microcavities within allochthonous Cambrian Epiphyton algal mounds in the upper Shady Dolomite (Shady Formation) of southwestern Virginia contain a preserved coelobiontic (cavity-dwelling) biota of probable late Early Cambrian age. The microcavities (range from 0.3 mm to 15.0 mm across (mean, 2.0 mm) and are constructed by overgrowth of Epiphyton fronds. Epiphyton dominates the coelobiontic biota, although other algae occur on the cavity roof and walls, including spherical micro-algae (?), crust-forming Girvanella and Cavifera, a probable endolithic alga found only in the fringe cements within microcavities. Globular Foraminifera (?) or foraminifer-like microorganisms, possible brachiopods and cylindrical borings also occur on or in the roofs and walls. Disarticulated, small inarticulate brachiopod valves, sponge spicules and grains bored by endolithic microphytes are in the sediment flooring many microcavities. This indicates that microboring algae or fungi, sponges and inarticulate brachiopods, probably inhabited the microcavities. Traces produced on the surface of the sediment in some microcavities and small spines show that vagrant organisms were moving within or through cavities. Localized areas of Epiphyton have been planed flat, pointing to the presence of an unidentified grazing organism in the microcavities. These mounds occur stratigraphically above archaeocyathid patch reefs in the Shady (Dolomite) Formation. The mounds contain no archaeocyathids. The presence of coelobiontic organisms in Lower Cambrian algal mounds lacking a skeletal framework suggests that coelobiontic organisms were not restricted to skeletal reefs but that at least by the end of the Lower Cambrian they had exploited the cavity habitat in algal mounds.