Burrows and Trails from Pennsylvanian Rocks of Texas

In another paper,1 we have called attention to the existence of snail burrows in the Brazos River sandstone, a member of the Pennsylvanian Garner formation of Scott and Armstrong,2 or the lower Mineral Wells of Plummer and Moore. This paper describes other burrows, some molluscan and some of arthtopod origin, from the same sandstone. All were collected at the exposure on U. S. Highway 80 N, at the escarpment formed by the Brazos River sandstone, west of Millsap, Parker County, Texas. Locality is not indicated in the descriptions. Some readers may question the desirability of distinguishing such problematic fossils as these by generic and specific names. The answers to this question are two, one practical and one biologic. On the practical side, it seems evident that in the Brazos River sandstone, as in many other sandstones and sandy shales, the recorded fauna consists chiefly or wholly of burrows and trails. If these traces possess the uniformity of character which justifies their use in interpretation and correlation, they can be satisfactorily used only in the form of genera and species. That the traces do possess such uniformity seems evident, even from the small collections at hand. Each group to which a name is applied seems stable within a range no greater thant that of ordinary petrifactions. Our observationsand those of biologists whom we have consulted, indicate that burrowing annelids, molluscs and arthropods make traces of definite and stable character. In many cases, distinctions are constant between species; in others they hold for genera. In snails, crabs and some annelids, we have found both generic and specific distinctions in trails, correlation with genera and species of living organisms. In short: in modern seas, characters of burrows and trails have observable taxonomic meaning. It seems only proper for us to assume similar meaning for fossil traces, and to give them taxonomic recognition.