The modern Niagara River was initiated as a multi-outlet river-lake system following the last ice retreat from the area about 12,300 yr B.P. This system extended from Early Lake Erie to the contemporaneously formed Glacial Lake Iroquois in the Ontario basin. The last major ice advance and one subsequent glacial oscillation associated with the ice retreat are recorded in sequences of glaciolacustrine deposits and till along the present Gorge wall and within older bedrock spillways. Dated wood overlying Iroquois silts and till within the Lockport spillway, east of Niagara, suggest that the multi-outlet (Lake Tonawanda) phase of the drainage ceased about 10,900 yr B.P. with concentration of the outflow, and hence major gorge recession, at Lewiston. Radiocarbon analysis of mollusks from river gravels at the top of the Niagara Gorge at Whirlpool Park indicate that cataract recession from Lewiston to this site of intersection with the much older buried St. Davids Gorge occurred after 9800 yr B.P. Lake Tonawanda persisted near the present site of Niagara Falls until about 1,000 yr ago; however, dated mollusks imply that deposition here was interrupted by intense scouring shortly before 3800 yr B.P., which may have been a response to the closing of the North Bay outlet of the upper Great Lakes and consequent large increase in discharge through Lake Erie.
Mollusks which occur in the ancient Niagara River gravels are well preserved and distinctly zoned. The Lake Tonawanda fauna, heretofore undescribed, includes about 15 species, all of which are extant in the region.