100 SIXTEENTH REPORT. 



when crowded to contact. There is for each pair of coasts one distance, 

 and of course only one, by which they are separated when their curves are 

 concentric. This distance is easily determined by experiment. Between 

 North America and Africa it averages 200 to 300 miles, between Africa and 

 South America it is about 300 miles. There are a few places, as between 

 the Brazilian coast and that of upper Guinea where the distance is so small 

 as to be almost negligible. 



One reason why the submerged border is not to be relied upon is that it is 

 rapidly changing. 



Whereas denudation proceeds on all exposed surfaces, marine deposition 

 is confined for the most part to a narrow strip about the borders, and in this 

 relatively small sedimentary area the rate of building up must be many 

 times the rate at which the general continental surface is being lowered. 

 Not only this, but owing to the irregular distribution of rivers and currents 

 sedimentation is of necessity most irregular. These factors are at work 

 constantly modifying the depth contours near the land and working always 

 in the direction of heterogeneity so that after the lapse of any considerable 

 geological time it is not to be supposed that the hundred fathom depth will 

 retain its former contours. 



The indications of severe denudation in northern America and Europe 

 during Tertiary time, culminating in the exceptional conditions of the glacial 

 epoch, point to the oceans of similar latitudes as areas of even greater sedi- 

 mentary blanketing, and the inference appears to be well borne out by the 

 bathymetrical chart. There is a greater area within the hundred fathom 

 curve to the east and south of Newfoundland than is occupied by that island 

 itself. From Cape Hatteras northeast the hundred fathom line runs, ex- 

 cepting inlets, at an increasing distance from the shore. Upon the opposite 

 side of the ocean, beginning near the deep in the southern part of the Bay 

 of Biscay, the line keeps well out to the west around Ireland and the islands 

 of the Scottish coast, bending east and south and reaching the coast of 

 southern Norway after including nearly the whole of the North Sea. 



The 2000 fathom area in the North Atlantic is noticeably restricted, being 

 encroached upon from the west and the north and broken in the middle by 

 the Dolphin Ridge. North of the fiftieth parallel there is little 2000 fathom 

 water and what there is diminishes to the northwestward and northeastward 

 with converging boundaries, these prolongations hinting of the division of 

 the ocean to the west of Greenland and east of Iceland. 



The 1000 fathom outline is likewise considerably restricted. One finger 

 pointing up in Davis Strait, a second to the west of Iceland, and a third and 

 fourth between Iceland and Ireland. 



For all these depths the Atlantic is thus seen to shoal out as we proceed 

 toward the north and toward the land. All these contours are inseparably 

 connected with the present major distributions of land and sea, and yet 

 they show individuality, each from the others. It is as if all had been pro- 

 foundly altered, but by no means equally, in short as if the North Atlantic 

 were in course of irregular filling up, which it is, of course, the process accel- 

 erating wdth latitude, and the natural inference is that we are viewing the 

 effects which the rigors of northern climate have had in the tearing down of 

 land and the transporting of materials. That the evidences of heavy sedi- 

 mentation are here observed at such great distances from land is very likely 

 attributable to transport by floating ice. How much of the alteration of 

 the bottom must be set down to crustal movement is a question unanswered; 

 even the Dolphin Ridge, too far separated as it is from land by deep areas 



