THE VARYING CHARACTER OP ANCIENT SHORES. 77 



Many of the upper beaches overlie drift deposits, but those of the lower 

 elevatious are more likely to rest upon stratified clay — the sediments carried 

 into the deeper waters whilst the lakes were at higher altitudes. The char- 

 acter of the materials underlying the beaches is commonly the same as that 

 forming the surface of the plain in front of the ridges ; but its structure is 

 best shown in sections exposed by the subsequent erosion where streams cut- 

 ting through the ridges cross the plain. When such streams have been large 

 rivers, as has often been the case, there may be some trouble in tracing the 

 continuity of the beach, especially across a broken country, as a portion of 

 the valley may be older than the beach, which may swing around and skirt 

 the embayment, or form a bar across it. Or again, the beach may be only 

 represented by conical or other shaped sand or gravel hills, which were delta 

 deposits at the mouth of a former river. Such delta deposits may not rise 

 to the level of the former body of water. 



With the varying conditions here set forth, which the shore-lines undergo, 

 the traveller, in coasting around the old lakes, can rarely proceed more than 

 a few miles without meeting obstructions. When the beaches ax-e a consid- 

 erable distance apart, with perhaps only fifty or a hundred feet of difference 

 in their altitudes, there is a liability of getting off one series and upon 

 another. Consequently it is often necessary to resort to accurate levelling, 

 allowing for reasonable variations in the height of the beach, and the diff- 

 erential elevation of the region, since the waters have receded from the 

 former shores. 



In some regions the former expansions of the lakes were occupied by archi- 

 pelagoes. Consequently, there is an absence of continuous beaches, and the 

 explorer must depend upon following the plain, which formerly constituted 

 the lake-floor, finding here and there a fragment of the ancient beach, either 

 upon the coast of the mainland or upon that of an island. Here again, it 

 may be necessary to resort to accurate leveling to identify the beaches. 



Whilst steep coast-lines may be followed through wooded regions, it is 

 most difficult to trace satisfactorily a beach across such a country. The 

 greatest difficulties are found where the ancient beaches enter regions that 

 are composed of hills of crystalline rocks, more or less wooded, and iuter- 

 spers d with numerous lakelets. In such places, there are numerous gravel 

 hills whose relationship to the old shores is not readily discernable. 



In some places, the surface of the beaches is composed of nearly clean 

 gravel or sand ; elsewhere, from some admixture of clay, it becomes 

 more or less earthy soil, to a depth of two or four feet, somewhat obscuring 

 the beach structure. Again, there may be coarse stones resting upon its sur- 

 face, as if these had been forced up after the beach had been formed, by a 

 slight rise of the waters, or by the action of coast-ice, pushing them up. 

 However, these must not be mistaken for the more ancient gravel beaches, 



