32 



steep and much-gullied slope of drift. This place is in 

 an almost direct line with the prolongation of the older 

 cliff lines at the whirlpool, and it seems impossible to 

 doubt that the gorge extends through to the break in the 

 escarpment south of St. David. One of the faint terminal 

 moraines of this region crosses its northern part and forms 

 the highest part of the filling. 



The greatest depth found in the whirlpool by Spen- 

 cer's soundings is 126 feet (38-4 m.). This is in the 

 middle of the pool and of the upper part of the ancient 

 gorge, where the river in its recent gorge making had 

 only soft drift to remove and no vertical fall with which 

 to bore the rocks at the bottom. This depth belongs, 

 therefore, to the old buried gorge, and, indeed, may not 

 show its full depth in the rock. 



Dr. Spencer made a boring into the drift filling of 

 the old gorge at a point about half a mile ( • 8 km.) north- 

 west of the whirpool, but at a depth of 269 feet (82 -m.) 

 encountered difficulties that stopped the work. The 

 boring was started on the general level of the plain and 

 ended at a level of about 24 feet (7-3 m.) above the water 

 in the whirlpool. No rock was encountered, the material 

 being mainly till, sand and some gravel, with boulders 

 at the bottom. While this boring did not reach the rock 

 bottom of the old gorge, it nevertheless strongly confirms 

 the conclusion that the gorge continues to the northwest. 

 The discovery and re-excavation of the head of the 

 old buried gorge by the modern river appears to have 

 been merely an accident of topography. When the river 

 first began to flow, the lowest line across the plain happened 

 to carry the river over the upper end of the buried gorge, 

 and when the falls had gnawed back to this point they 

 quickly cleaned out the drift materials and resumed rock 

 cutting by a vertical cataract at the southeast side of the 

 whirpool. 



Not only is the ancient gorge filled with glacial drift, 

 but at one point in Bowman ravine north of the electric 

 railway embankment, glacial striae and polishing were 

 found on the west wall of the gorge 90 feet (27-4111) below 

 the top, showing clearly that the gorge was occupied by a 

 current of the ice sheet before it was filled with drift. 



Grabau and others who regard the buried gorge as 

 of pre-glacial age point to the widening towards its mouth 

 south of St. David and attribute this to the subaerial 



