AND TRANSPORTING AGENT PREST. 339 



To one class belong the scratches caused by the expansion of 

 harbor ice holding large stones which are pushed up from shoal 

 water. These are most prominent in the best protected positions, 

 where it appears impossible for glaciers or drift ice to act. 



The other class of marine striae is formed by large boulders 

 lying usually at high watermark, and which have been rolled 

 down from frost-shattered cliffs near by. They are pushed back 

 by ice jams or by ice hurled against them in a scorm, and move 

 a foot or a few inches at a time. These strite are partly pro- 

 tected from obliteration by the boulder itself. 



In regard to the question of erosion by icebergs, the first 

 point to be considered is whether bergs carry stones in positions, 

 suitable for eroding. 



Observers in the far north, as well as those who have exam- 

 ined glaciers in more temperate latitudes, maintain that debris 

 falls into cracks, or is lodged on the surface of those ice masses 

 and are then carried to sea when the bergs are detached. But 

 it is plain that stones attached to the sides and bottoms would 

 melt off during their long voyage, and this contention is sup- 

 ported by much negative evidence. Although I saw many 

 overturned bergs I saw no stones attached. I therefore feel 

 compelled to fall back on the theory that bergs striate the sea 

 bottom only by bringing their great weight to bear on loose 

 rocks. Should such striae have been formed before the old shore- 

 lines were raised to their present positions, they could not 

 possibly have emerged above the polishing influence of the field 

 ice., Being formed only in the positions afterward exposed to 

 the wear of pan ice. I am thoroughly convinced that such a 

 phenomenon asstrise by ice-bergs does not exist above the sea level. 



A rising coast as in Labrador, exposes a well worn rock 

 bottom, smoothed by ice action during the preceding subsidence ; 

 and in an exposed position all protecting debris is speedily- 

 washed into deep water, and oil signs of berg erosion obliterated. 

 A sinking coast carries its strife with it, if such striae can be 

 retained long enough to get below the intense ice action seen ia 

 Labrador. 



PROC. & TRANS. N. S. INST. Sci., VOL. XL TRANS. X. 



