CHANGES OF LEVEL OF NORTH AMERICAN COASTS. 159 



in connection with tlie evidence afforded by the better known southern 

 l)arts of the shore, witli its flooded valleys and submerged forests, it 

 seems to me tliat the only tenable view is that of recent and extensive 

 subsidence, perhaps amounting in the Hudson Bay district to 1,000 feet 

 or more. 



Pdcific Coast. — On the western coast of North America a comparative 

 absence of considerable river valleys makes the interpretation of the 

 coastline movements more difiicult than on the eastern shore. ^lore- 

 over, the streams which exist in that field flow from a country wdiich is 

 as yet not far advanced toward baseleveling, and therefore have their 

 channels in most cases so steep that the penetration of the sea, with a 

 given amount of downsinking, would be much less than on the Atlantic 

 slope. Furthermore, the studies of recent changes of level along the 

 Pacific have aff'orded as yet but little evidence, such as raised beaches 

 or submarine forests. In a word, the problem, so far as this shore is 

 concerned, is not ripe for discussion. I shall therefore note but few 

 points which seem to me to have an indicative value in connection with 

 the question under consideration. 



The most important fact concerning the Pacific coast which bears upon 

 our problem is that the continental shelf, which is such a conspicuous 

 feature along the Atlantic coast of Europe and North America, appears 

 not to exist on that side of the continent. An examination of the marine 

 soundings shown on the charts makes it probal)le that there is no such 

 mass of recent sediments off' the shore as exist in the submerged plain 

 of the Atlantic coast or the emerged portion of it Ij'ing in the southern 

 states of this Union. 



The absence of a characteristic marine shelf ma}^ be accounted for in 

 either of three ways: By the relatively small amount of land detritus 

 borne into the sea at this coast; by a recent subsidence of the shoreline 

 to such an extent tliat the slielf has been lowered to sucli a depth that 

 tlie rare oflsliore soundings do not reveal it, or l)}"" the introduction of the 

 shelf tlirough elevation into the body of the land where its characteristic 

 form has l)een lost through the recent mountain-l)uilding which has 

 affected this ])art of the shore. 



Although the Coast range is of late Tertiary origin, it does not seem 

 likely that the rocks which are folded in it are of sufficient horizontal 

 extent to explain the lack of a submarine shelf of the ample dimensions 

 required by the large amount of erosion whicli the agents of sea and 

 land have accomplished on the Pacific slope. Large as has been the 

 amount of this wear, it is, however, less than that which has taken place 

 upon the Atlantic versant of the continent, which has evidently been 

 much longer exi)osed to degradation and i)rol)abl3^ also has been on 



