Karst

Gray, R. E. and Turka, R. J. “Shallow Karst in a Breached Anticline”, Hydrogeology and Engineering Geology of Sinkholes and Karst - 1999, Beck, Petit & Herring (eds) © 1999 Balkema Rotterdam.

Knott, D. L., Newman, F. B., Rojas-Gonzalez, L. F., and Gray, R. E.  "Foundation Engineering Practice for Bridges in Karst Areas in Pennsylvania",  Applied Karst Geology/Proceedings of the Fourth Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Karst.  Rotterdam:  A. A. Balkema, 1993.

Gardner, G. D. and Gray, R. E.  "Tracing of Subsurface Flow in Karst Regions Using Artificially Colored Spores",  Bulletin of Association of Engineering Geologists, vol. 13, no. 3 (Summer 1976).