SUMMARY AND CONCLUSIONS 225 



stretches with exaggerated gradients, separated by reaches of only gentle 

 decline, forming steps. Occasionally outlying portions of the continental 

 slope seem to become terraces or more deeply submerged plains of 

 slight inclination, with promontories extending from them, overlooking 

 the deep valleys ; as, for example, the valley of the Chesapeake passes 

 over two precipitous declivities of 2,000 to 3,000 feet each, and it is 

 traceable for upward of 60 miles from the edge of the continental shelf, 

 where it enters an embayment at the foot of the continental slope. The 

 coves or gulfs of the Delawarean, Hudsonian, Fundian, Cansoan, and 

 Laurentian valleys are each characterized by the deep steps just noted. 

 So also there are amphitheaters indenting the edge of the coastal plain 

 submerged far away from present shores. These valleys traceable down 

 the continental slope are in size no greater than those of existing rivers. 

 The phenomena of all these strikingly repeat themselves. The valleys 

 seem quite independent of mountain folds and are more or less at right 

 angles to the orographic S3^stem, though the rivers entering them may 

 either cut across the mountains or occupy depressions parallel with 

 them. 



The incisions in the floor of Baffin bay and Davis straits are magnifi- 

 cent examples of coves, canyons, and valleys indenting the land masses, 

 though they are now sunken to form fiords. The Greenland-Icdand- 

 Shetland ridge, which comes near the surface of the sea, is also incised 

 by similar vallej^s trending in opposite directions toward both the Arctic 

 and Atlantic basins, so much so that it would not be a bold prediction 

 to expect to find submarine river valleys descending the North Atlantic 

 plateau if close soundings were made. Even these deep gulfs have been 

 discovered far north, off Spitzbergen. Thus, while there are local varia- 

 tions, the exact phenomena of land features are found from tropical to 

 arctic zones and from regions of volcanoes to those of glaciers, whose 

 forces are subordinate to atmospheric action, which appears to have 

 stamped itself upon the great submarine slopes of the continent. 



Passing over the old topography of the continent to its margin, it 

 appears that the features described are newer than the remnants of the 

 Miocene accumulation of the coastal plains; but the period when the 

 broad vallej^s were deepened into canyons was subsequent to the Lafa3^ette 

 epoch, and while of shorter duration than the ages which gave rise to 

 the general features, was sufficiently long to form the amphitheaters, 

 canyons, and valleys which we have described. These last appear to 

 belong to the general period of glacial deposits, and suggest a recent 

 great elevation of the land, following out the teachings of Lyell, that 

 where now the sea is the land once stood. The minor inter or post 



