ABSTRACT

"Rudistid reefs" and the "rudistid reef facies" have long been referred to in conjunction with the Edwards formation of Texas. The general geology of the Edwards is reviewed with emphasis on the lithologic and faunal characteristic of the biostrome facies.

The reefs have been divided into those structures which have undergone preservation by calcification and those which have been replaced by siliceous material. The siliceous reefs offer an unusual type of preservation, and the occurrence of new species and extensions in geologic range of other species in these reefs is noted.

A comparison between the calcareous and siliceous faunas shows that the variations are mainly due to slight environmental differences rather then to mode of preservation.

The paleoecology suggests that these biostromes were deposited in a relatively shallow (10 to 20 fathoms, epicontinental sea. The waters were warm, clear, of normal salinity, and populated by an abundance of pelecypods, gastropods and corals. The pelecypod concentrations attracted a large number of carnivorous marine snails.