256 bulletin: museum of comparative zoology. 



contour, could under normal conditions, transport large boulders from 

 the adjacent depths and lodge them, delicately poised, on the summit of 

 the ridge. The explanation by floating ice would leave out of account 

 the great rarity of trap boulders, though these should be the commonest, 

 since, during submergence, the only shoals for many miles around 

 whence floating ice might derive rock-fragments other than glacial 

 erratics, would be underlain by the trap of the present hills. Still less 

 would the sudden cessation of this sort of deposition at the 265-foot 

 level as the land arose, be explained. Finally, both hypotheses suffer 

 from the difficulty that boulders, perched on the ridge-summit as we now 

 see them, could not be left in situ if the rate of uplift were anything 

 else than catastrophic. A single heavy storm from the southward would 

 doubtless suffice to sweep all loose material from their precarious posi- 

 tion. The conclusion that the boulder-covered zone has never been 

 submerged since the general ice-sheet retreated from the country, can- 

 not be escaped. On the other hand, the boulderless zone is a wave- 

 swept zone. 



Other evidences for former submergence of the lower zone are clear 

 and convincing. The smooth, unbroken surfaces of the roches moitton- 

 nees above 205 feet contrast strongly with the jagged and riven ledges 

 below that level. At the upper limit of the boulderless zone, low, but 

 steep and rugged cliffs look northward over frequent pockets and 

 graded slopes of well-rounded pebbles. Similar deposits were observed 

 at 145, 155, and 175 feet, while an unusually fine boulder-beach fifty 

 yards long and twenty in width occurs at 205 feet. The boulders, 

 averaging six inches in diameter, are not covered with vegetation, and 

 bear remarkable resemblance to the raised beaches of Hogland in the 

 Gulf of Finland. Such beaches are rare on both Ice Tickle Island and 

 on Rodney Mundy Island. That they were here not discovered more 

 plentifully is due to the general steepness of the ridges and the conse- 

 quent lack of places of lodgment for loose material ; to the hardness of 

 the rocks hereabouts, coupled with the shortness of the time allowed for 

 beach-building; and to the abundance of moss and other peat-formers 

 that develop thick vegetable mantles over most graded slopes. An indi- 

 cation of the great variety of form assumed by elevated sea-chasms, 

 benches, and boulder-deposits in the wave-swept zone at other localities, 

 will appear in the following pages. 



Occasionally it was found that single boulders in exposed situations 

 occurred below the accepted level of the highest shore-line. These were 

 either too large to be moved by the waves, or had rolled down from the 



