The Connecticut Lowland is old, but its ancient drainage lines were buried by the deposits left in glacial Lake Hadley. The river’s present course was established upon these lacustrine sediments, and the inner valley plain is excavated in them. Before entrenchment took place, the south-flowing reach of the river above Millers Falls was deflected westward across the lake plain by the delta of Millers River. It was turned southward once again by the trap ridge near Turners Falls. The river soon cut through the unconsolidated lake beds and found that it was out of its pre-glacial channel. The delta of Millers River had diverted the water from the old rock valley beneath the Montague sand plain, across a rock divide, and into the pre-glacial valley of Falls River. The lake-fill in Falls River has been almost completely removed, and Turners Falls now mark the spot where the Connecticut pours over the bank and into the channel of its pre-glacial tributary. The falls have receded upstream several hundred feet and have cut a deep gash in the Triassic rocks.
Pl. 7. Gorges, in highland and lowland alike, were formed when the rivers were superimposed on coherent rock.
a. View of the Deerfield River gorge emerging on valley lowland as seen from Mt. Sugarloaf.
b. View of the French King gorge as seen from the bridge.
Turners Falls are the product of a series of coincidences. First, the ice sheet and Lake Hadley buried all established drainage lines and forced the streams to adopt new routes over the bared lake bottom. While the lake existed, Millers River threw a weak obstruction in the path of the Connecticut, diverting it to that part of the lowland where one of its pre-glacial tributaries had excavated a slender rock gorge along a fault plane. The river washed the lake deposits out of the gorge, exposed the old bank of Falls River, and was busily cutting a new gorge back into this bank when the dam was constructed and its erosive activities were suddenly arrested.
The French King Bridge
The highway from Greenfield to Athol and Fitchburg passes Turners Falls and crosses the Connecticut River near Millers Falls by way of the French King Bridge. Here the roadway is more than 130 feet above the water level. A picnic ground and parking place at the west end of the bridge make it a particularly attractive place to stop and enjoy the view upstream towards Northfield.
The river occupies a narrow rock gorge for a mile north of the bridge, but at that point the valley widens out. This entire section of the river’s course was established on the old bed of glacial Lake Hadley; but after the unconsolidated deposits were washed away, the stream found itself flowing along the weak contact between the Triassic conglomerate on the west bank and the metamorphic rocks of the highlands on the east bank. The river deepened its channel on the weak contact zone and made the scenic cut over which the bridge was built.