PHYSICAL AND CLLMATAL CONDITIONS. 107 



To the same effect is the following by Capt. Fieldeu : * 



" Sm-icc, moved up and down by tidal action, or driven 

 on shore by gales, was found to be a very potent agent in 

 the glaciation of rods and pehhkfi. The work was seen in 

 progress along the shores of the Polar IJasin. At the 

 south end of a small island in JMackcliff bav, lat. 82'' 30' 

 N., the bottoms of the hummocks, some eight to fifteen 

 feet thick, were studded with hard limestone pebbles, 

 which, when extracted from the ice, were found to be 

 rounded and scratched on the exposed surface only. 



" On shelving shores, as the tide recedes, the hummocks, 

 sliding over the subjacent material down to a position of 

 rest, make a well-marked and peculiar sound, resulting 

 from the grating of included pchhles, laifk the rock// Jioor 

 beneath, or in some cases on other pebbles included in 

 drift overlying the rock." 



Action of this kind now taking place along northern 

 shores must have been carried over all the submerged 

 portions of the continents in the l*leistocene, and affords 

 the only rational mode of accounting for the general 

 striation, not dependant on local glaciers and related to 

 the lines of valleys, but occurring on the surfaces of the 

 plains, and on the summits exposed at various times to 

 the action of ice carried by the northern currents. 



hatgc boulder of sandstone deiiositcil \>y modern iee on a sand-bank — 

 Pelitt'odiac liver, New Brunswick. 



* Nares' Arctic Voyage, Vol, II., p. 34.3, quoted, along with other 

 examples, by Mr. Milne Home. 



