THP] SUCCESSION OF DEPOSITS. 41 



The boulder-clay locally presents, as above stated, indi- 

 cations of successive layers, and it occasionally contains 

 surfaces on which lie large boulders striated and polished 

 on the upper surface, in tlie manner of the pavements of 

 boulders described by Miller, as occurring in the Till of 

 Scotland. Tliese appearances are, however, rare, and few 

 opportunities occur for observing them. 



A very general and important appearance is the polish- 

 ing and striation of tlie underlying rocks usually to be 

 observed under the boulder-clay, and which is undoubtedly 

 of the same character with that observed under Alpine 

 glaciers. This continental striation or grooving is obvi- 

 ously the effect of the action of ice, and its direction 

 marks the course in which the abrading agjent travelled. 

 This direction has been ascertained by the Canadian and 

 United States surveys, and by local observers, over a 

 large part of America, and it presents some broad features 

 well deserving attention. A valuable table of the direc- 

 tion of this striation is given in the " Geology of Canada," 

 which I may take as a basis for my remarks, adding to it 

 a few local observations of my own.* The table embraces 

 one hundred and forty-five observations, extending along 

 the valleys of the St. Lawrence and the Ottawa and the 

 borders of the great lakes. In all of these the direction 

 is south, with an inclination to the west and east, or to 

 state the case more precisely, there are two sets of striae, 

 a south-west set and a south-east set. In the table 

 eighty-four are westward of soutli and fifty-eight are 

 eastward of south, three being due south. It further 



* See also, for the western districts, Whittlesey's Memoir in the 

 Smithsonian Contributions, and Newberry's Report on Ohio ; Papers 

 by Dr. G. M. Dawson on the Plains of N.W. Canada in Journal of 

 Geol. Soy. of London and Trans. R.S. Canada. 



I 



