The Virgelle Sandstone is a geologic formation overlain by the Two Medicine Formation."Geological Setting," Trexler (2001); pages 300-301. It formed from the beach sands exposed on northern and western shores of the receding Colorado Sea.
Footnotes
References Trexler, D., 2001, Two Medicine Formation, Montana: geology and fauna: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, pp. 298–309.