Two thick sequences of ancient glacial and glacial marine rocks, the late Proterozoic Mineral Fork Formation of Utah and the Late Paleozoic Whiteout Conglomerate of West Antarctica, reflect similarities and differences in temperature regimes of the glacial delivery systems, climatic settings in the zones of ablation, and nature of the glacier interfaces with the depositional environments. Both units attain thicknesses of about 1,000 m and both are segments of widely distributed glacigenic deposits covering thousands of km 2 . They appear to represent significant erosion of platformal areas beneath basal ice at or near its melting point. In the Mineral Fork Formation, facies patterns indicate supraglacial melt-out, sediment gravity flow, and deposition from meltwater streams, all characteristic of glacier ice where the climate is subpolar or temperate in the zone of ablation. The vertical sequence, which includes subglacial tills, supraglacial melt-out facies, and a complex glacial marine facies, indicates multiple advances of a grounded ice sheet along the margin of a craton, and final retreat accompanied by a marine transgression. In contrast, the Whiteout Conglomerate lacks facies indicative of supraglacial melting; the absence of meltwater-generated fluvial and plume deposits is especially striking. Rather, subglacial melt-out from grounded ice and basal melting of ice shelves and perhaps icebergs, all accompanied by vertical settling, are indicated. Lateral changes represent a regional transition from grounded marine-based glaciers at the pressure melting point in the basal zone to a shelf of polar ice warmed sufficiently at the base to release sediment there by melting as well as by iceberg calving. The study of thick ancient glacigenic sequences accumulated on subsiding continental margins provides information not yet obtainable from sedimentary piles of Quaternary age.