152 THE FLOOR OF THE OCEAN 



Such material at the angle of rest will yield rapidly if its back 

 is even gently brushed by a down-hill current. 



Now, let us leave the laboratory and go outdoors again, to 

 find other facts and potential tests relating to the Glacial- 

 control hypothesis. 



In Figure 81, a map of Georges Bank, the submarine con- 



+ GLACIAL TILL 

 CANYON 



60 Nautical M.lcs 



FIGURE 8l. MAP OF GEORGES BANK, SHOWING LOCATION OF GLACIAL TILL 



(crosses) AND OF SUBMARINE canyons (at barbed arrows). 



tours or isobaths are drawn at intervals of ten fathoms. Over 

 the southern half of the bank Professor Shepard has dredged 

 up gravels like those just outside glacial moraines. 19 At six 

 points, marked with crosses, he found boulder-clay or till, a 

 characteristic subglacial deposit. These facts suggest that the 

 terminal moraine of the North American ice-cap lay across the 

 middle of the bank, along a roughly east-west line; and that 



