An unusual biota of reef-building organisms occurs in biohermal limestones of Virgilian age in the Sacramento Mountains. Some are organisms not known before from this area, and the reef-building potentialities of others have not previously been recognized.

Tubular unchambered Foraminifera (Paleonubecularia and Calcitornella) together with algae (Girvanella and others) form extensive (several square feet) flat to hummocky "pavements" and large "heads." A distinctive tabular siliceous (?) sponge (Stereodictyon Finks, 1960) occurs as fragments of three-dimensional reticulate meshwork up to 18 inches long and 1½ inches thick. Stromatoporoids have been considered to be rare in Pennsylvanian rocks, perhaps only because the Pennsylvanian reef facies is not well known: one genus (Parallelopora) occurs here as large hemispherical colonies and as encrusting masses and fragments. Branching stems and tabular to domal crusts composed of cellular tissue and cone-shaped radiating tubes are tentatively referred to a Russian genus of hydractinoid ( aleoaplysina Krotov; Riabinin, 1955). In addition to several varieties of stromatolitic algae and algal plates, there are finger-like masses made by a filamentous alga (Girvanella), nodular algal masses (Ortonella), and a branching encrusting alga (Tubiphytes Maslov, 1956). Dark-colored fibrous radiate calcite resembling the problematic Stromatactis of lower Paleozoic reefs occurs in tabular encrusting masses with smooth bottom surfaces and botryoidal upper surfaces.

These limestones were described by Plumley and Graves (1953) as a "cryptozoon stromatolitic reef." Wray (1959) and Konishi and Wray (1961) ascribed these biohermal buildups to the sediment trapping and binding effect of an erect-growing leaf-like calcareous alga (Eugonophyllum) similar to Ivanovia and Anchicodium.

Neither the stromatolitic algae nor the leaf-like algal plates appear to be capable of constructing these bioherms by themselves. More effective reef-builders are present: frame-builders (tubular foram "heads," stromatoporoid, and Stromatactis); sediment-catchers (tabular sponge); detritus-binders (hydractinoid, Tubiphytes); and sediment-binders (tubular foram and algal "pavements"). These and the small but significant amounts of reef-debris deposits indicate that these were true reefs growing above wave base.

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