This paper has to do with petroleum and natural gas prospects of that great group of clastic, mainly transition-zone, sediments that occupy a stratigraphic position between the Precambrian surface and the overlying Paleozoic formations, within the interior of North America, with particular reference to those sedimentary basin margins that flank the Precambrian Shield of North America and the related buried Precambrian islands. The example that is best known to the writer is the so-called "Granite Wash" of northern Alberta which is taken as a "field laboratory" example for comparison with other known, as well as unknown, sands in those parts of the basins of the interior of North America that are likely to be prospective at this horizon. The Granite Wash and related sands re defined lithologically and their age relationships to overlying and underlying rocks discussed, with particular reference to the possible origin, lithology, structure, paleotopography, and the tectonic history of the underlying Precambrian surface, on which they depend for their occurrence and development as reservoirs. The anticipated future in Western Canada and elsewhere in North America with particular reference to the parts that should be played jointly by geophysics and geology are also discussed.