Neoproterozoic diamictites of the Vreeland Formation exposed in the Snake Indian and Wapiti Pass thrust sheets of the central Rocky Mountains, northeast British Columbia, form. a thick (350 to 2000 m) glaciogenic deposit within the passive margin succession of the Windermere Supergroup. They are the deposits of the younger worldwide episode of Neoproterozoic glaciation. Diamictites were deposited as laterally extensive sheets in a mid slope setting with minimal sediment reworking or transport by bottom currents. In the Wapiti Pass thrust sheet, the absence of dropstones and lonestones, in facies-equivalent and interbedded fine-grained strata, indicates there was little, if any, ice rafting during sedimentation. Diamictites are the deposits of unconfined debris flows derived from the slumping of glacial deposits near the shelf-slope break. In the Snake Indian thrust sheet, dropstones and lonestones indicate ice rafting. Diamictites formed from both unconfined debris flows and the "rain-out" of ice-rafted and sediment plume material. Deposition of thick diamictites in the Mount Vreeland area was probably localized by syndepositional, west-side-down normal fault(s). Diamictites contain abundant extrabasinal (felsic and basic intrusive, volcanic, quartzite) and intrabasinal (argillite, sandstone, carbonate) clasts. They record a major source of material entering the Windermere depositional basin distinct from the basinal turbidite system of the southern Cordillera. The high volumes of glaciogenic sediment and large extrabasinal clasts indicate the transportation of massive amounts of material to the shelf-slope break by glaciers and glacial processes. Their deposition appears to be incompatible with the snowball Earth model for Neoproterozoic glaciation, with its thin patchy continental ice cover and the virtual elimination of the hydrological cycle. Locally, the diamictites are overlain by a thin deep-water limestone (cap carbonate). Olistoliths of platformal carbonates in the immediately overlying argillite indicate deposition of postglacial (cap) carbonates on the shelf to the east, continued deposition in a slope environment in the study area, and continued instability and fault-related uplift of the shelf edge. Detailed mapping of the southwest flank of Ice Mountain shows that carbonate olistoliths, rather than a carbonate platform, overlie the diamictites. No evidence was found of penetrative deformation, uplift or erosion of diamictites during the Neoproterozoic to support a previous interpretation of the Neoproterozoic "Vreeland High".