“Pebble counts” within a restricted grade-size range are used as an index of approximate lithologic composition of till and associated gravel. Materials eroded from outcrops within the area studied were deposited down-current in decreasing amounts, apparently depending largely on the relative rates at which those materials were reduced by crushing and abrasion. Also, their distribution was controlled strongly by topographic relief, with marked concentration along the major valleys.
The distribution pattern of Canadian (Precambrian) erratics shows no relation to an immediate source other than their probable distribution in the earlier drift. This fact supports the conclusion that the last glacier to occupy the area between the Valley Heads end moraine and the Ontario shore had its effective center of outflow within the Ontario basin.