DALY : GEOLOGY OF THE NORTHEAST COAST OF LABRADOR. 255 



headlands and hills where the surf from the open ocean can be felt on a 

 glaciated shore during submergence, the present lower limit of undis- 

 turbed glacial erratics marks with but subordinate error the highest 

 shore-line of postglacial submergence. 



For the first time during the cruise, conclusive evidence of the value 

 of the criterion on the Labrador shore was obtained at Ice Tickle Harbor. 

 It is of importance to review the conditions under which it was there 

 employed. These conditions are essentially the same as those found at 

 the numerous other stations occupied up and down the coast. 



The situation, topography, and bed-rock geology of the islands on 

 either side of the tickle have already been described (p. 213). The dark- 

 hued trap-ridges are dotted over with light gray gneissic boulders offering 

 strong contrast in color and composition with the ledges beneath. These 

 boulders are subangular, not water-worn, often greatly decomposed, and 

 have evidently lain long in their present positions. They are associated 

 with a small proportion of boulder-clay which is, in places, actively 

 creeping down the slopes. Occasionally the boulders are pei'ched and 

 may be easily rocked with the hand. All these boulder-covered ridges 

 are over 265 feet high. Those of less height are devoid of boulders; 

 those of greater height may be divided into a boulder-covered and a 

 boulderless zone separated from each other by the 265-foot contour. 

 (Plate 8.) 



That the boulders are truly glacial erratics, reposing practically where 

 the great Labrador ice-sheet left them, can hardly be doubted. The 

 only alternative origins which have suggested themselves are two in 

 number. Either the boulders, originally deposited elsewhere by the 

 land-ice, were thrown up by strong storm-waves, or they were brought 

 thither by floe- or shore-ice. In spite of the unlikelihood of these 

 hypotheses, it was held that evidence should be obtained that would 

 thoroughly test them.' The long ridge on the southern shore of Ice 

 Tickle Island threw ample light on the question, and serves as an 

 extremely good type locality for demonstrating the criterion. 



This ridge, over a mile in length, and generally about three hundred 

 feet in height (325 feet, measured barometrically at the highest point) 

 is a residual hill situated where a thick trap dike projects above the 

 softer gneisses. Its axial trend is roughly east and west. Its sides are 

 very steep, running together at a sharp edge, whence one looks directly 

 out over Hamilton Inlet on the south and over a deep valley and beyond 

 over the open sea north of the island. There seemed to lie no possibility 

 that waves breaking on the ridge, submerged to the 300-foot, or any higher 



