400 



the river valley where the newer waterway rejoins the 

 older. 



Two geologists, Hind and Chalmers have offered explana- 

 tions of the main causes whereby the St. John at Grand 

 Falls was deflected from its original course and forced 

 to carve out a new channel. Hind [2, pp. 31, 132 and 207-8] 

 writing in 1865, believed that following the Glacial period, 

 the whole region was submerged beneath the sea and that 

 during this interval of submergence the St. John valley 

 was partially filled with unconsolidated material. Sub- 

 sequently as the land rose, the river cut into and removed 

 this filling material but during this process of re-excavation, 

 the river at Grand Falls, as it cut its way through the 

 overburden, departed from the course of the original 

 channel and as a result eventually carved out a new 

 channel in solid rock. 



Chalmers [1] in various articles, advanced the view 

 that during the Glacial period the St. John valley was 

 largely filled in with both stratified and unstratified 

 material of glacial origin. After the final retreat of the 

 glacial ice, the unconsolidated material, in places as at 

 Grand Falls, formed dams that diverted the river from its 

 old channel and caused it to excavate a new channel 

 through solid rock. 



The general hypothesis favoured by the writer is that 

 during the Glacial period while the region was mantled 

 with ice, the St. John valley was also filled with ice and 

 comparatively little unconsolidated material was there 

 deposited. Later, perhaps during an inter-glacial period 

 if such occurred, but more probably during and after the 

 final retreat of the ice, the river for a variety of causes, 

 was overburdened with detrital material and as a conse- 

 quence largely filled in the pre-existing valley. At a still later 

 date, the river, no longer overloaded, re-excavated its 

 ancient channel except where for perhaps minor causes, 

 it was diverted and carved out new channels. In the 

 case of the new channel at Grand Falls, it is thought that 

 one factor that caused the river to form a new channel, 

 was the existence of a deeply cut channel in the case of 

 a minor tributary, Falls brook, coming in from the east. 



