The presence of algal limestone bodies in the Point Peak and San Saba Members of the Wilberns Formation (late Dresbachian to Early Ordovician) in the Llano uplift region of central Texas has been known for many years, but they have not been studied in detail. The relations between environment, fossil algae, and algal structures are not well understood, and the descriptive terminology is becoming more complicated.

The writer examined algal macrostructures together with their corresponding microfabrics and fossil algal flora from a paleo-oceanographic viewpoint. Several previously unknown microfabrics were found that reflect the growth patterns of various algal taxa in response to different hydrologic conditions. For example, fossil algae with wispy or tufted growth forms are found in nonlaminated algal macrostructures (limited hydrologic stress), whereas laminated macrostructures such as stromatolites exhibit tightly laminated microfabrics (considerable hydrologic stress). The various environmentally produced structures are found commonly in sequences that depict the long-term oceanographic history of the algal limestone buildups (reefs) from their inception (commonly in the sublittoral) to the r culmination (commonly in the intertidal). Four genera of fossil algae found in this study were Girvanella, Epiphyton, Renalcis, and Nuia.

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