2 20 SEA AND LAND 



Lake Superior less injury has been effected by the coastwise 

 wandering detritus, for the reason that the shore is more rocky 

 than that of the other basins, and as yet the platform at the 

 base of the cliffs has not been sufficiently developed to make 

 as continuous beaches as we find along the coasts of Lakes 

 Michigan, Erie, and Ontario. 



Where a coast-line has an irregular front which is bordered 

 b)- distinct salient capes or fringed with islands, the coastwise 

 migration of sediments under the influence of waves and cur- 

 rents is much less continuous and therefore less menacing to 

 harbors than where the shore is characterized by long, straight 

 line beaches. On the uninterrupted shores the march of the 

 detritus may be singularly steadfast; it may, indeed, be com- 

 puted from year to year as at a certain rate. A change of wind 

 may set the materials temporarily this way or that, but the 

 average movement is in most cases subject to no considerable 

 alterations in its course. Where, however, the shore-line is 

 embayed, the recesses form pockets in which the waste accumu- 

 lates and beyond which it cannot journey until the basin is filled 

 and the beach is extended across its front. Thus along the 

 fiord zone, where embayments are very numerous, the coastwise 

 marching of debris is hardly to be noticed, while on the sand 

 beaches farther southward we may trace a continuous procession 

 of detritus, often moving straight away along the shores for 

 scores or hundreds of miles. 



Where, as is generally the case in the fiord zone, there are 

 islands or shoals lying on either side of a considerable reentrant, 

 a curious action arises, which leads to the formation of 

 pocket-beaches. Wliere the islands lie in the manner which 

 favors the formation of pocket- beaches, they may prove useful 

 elements of protection to a haven. Where, however, they are 



