CONTINENTAL TERRACES AND SUBMARINE VALLEYS 153 



the fall-off to the Gulf of Maine was completely smothered 

 under the ice. There, according to the Glacial-control hypoth- 

 esis, no canyons or furrows should be discovered, and there the 

 relative smoothness of the isobaths confirms the deduction. On 

 the other hand, the many re-entrants of the isobaths along the 

 southern fall-off of the bank represent canyons. Figure 67 

 shows part of the sculptured belt of this south side in some 

 detail. Is it too much to argue that Georges Bank testifies to 

 a Glacial date for the excavation of at least a large majority of 

 the submarine valleys? 



Again, the hypothesis is supported by a fact stated on page 

 100: in average the continental shelf lies several fathoms deeper 

 than it should if this gentle slope had a profile of equilibrium. 

 In concrete illustration : at the fall-off or outer limit of the shelf 

 the water is something like 10 or 15 fathoms deeper than it 

 will be when the shape of the terrace has been stabilized by 

 waves and currents of the future. As Dr. Kuenen has pointed 

 out, the present departure from the profile of equilibrium is of 

 the magnitude expected to result from wave erosion of the 

 terrace sediments during the time of glacially lowered sealevel. 

 Furthermore, his calculations show that the layer of sediment 

 thus removed contained enough silt and sand to supply the 

 gullying bottom currents that operated during the long period 

 of glaciation. 



An observation by Dr. Stetson is significant in this same 

 connection. The Glacial-control hypothesis implies that along 

 the outer part of the continental shelf the mud and finer sand 

 should have been specially liable to be caught up and removed 

 by the turbulent waves at the lowered sealevel ; hence the super- 

 ficial sediment of that outer belt should by sampling be found 

 to be coarser than the average sediment now being deposited 

 on the shelf. According to Dr. Stetson's researches in field and 

 laboratory such is the fact. 



