Fig. 138 — Photograph looking north-west towards St. Davids showing the excessive en* 

 largement of themouthof the preglacial channel. 



388 ft. 



PlG. 139 — Section, drawn to equal vertical and horizontal scale, showing enlargement of 

 Niagara gorge on the east side at its mouth at Lewiston: 1, Niagara limestone, 

 20 to 30 feet ; 2, Niagara shale, 70f eet ; 3 , Clinton limestone, 20 to 30 feet ; 4, Clinton 

 and Medina shale, 70 feet ; 5 , Quartzose Medina sandstone, 20 to 30 feet ; 6, softer 

 Medina sandstone, 120 feet above water level. 



