160 (Co Ale COIN ON 
continuity of strata is shown. It will be seen that inthe section 
AB, built during the period of retreat of the shelf front from A 
to B, the topset beds will pass laterally into pelagic deposits, and 
that in the section BC, built during the period of advance from 
B to C, the first-formed strata will pass somewhat rapidly through 
foreset beds into pelagic deposits. In the later-formed strata of 
the section BC, however, the foreset portions will assume greater 
importance, the transition to pelagic deposits taking place in the 
deeper water farther seaward. 
STRUCTURE OF A SHELF BUILT DURING NEGATIVE MOVEMENT 
Negative movement generally involves uplift of the adjacent 
lands as well as of the sea floor. So erosion will as a rule be revived 
and the supply of waste increased. Also as the sea retreats the 
former surface of the shelf will be subject to subaérial and marine 
erosion, producing a further supply of waste. Negative movement 
will therefore be generally accompanied by heavy sedimentation 
on the continental slope. 
It is conceivable, therefore, that the shelf may grow seaward 
with sufficient rapidity to maintain its edge at the usual depth 
throughout a period of rather rapid movement. During such move- 
ment the width of the shelf (measured from the ever-changing 
shore line) may diminish, remain constant, or even increase. In 
the first case the topset slope will be steepened by submarine 
erosion, and in the last case it will become less steep owing to 
deposition of topset beds. With constant width will go constant 
slope, with neither deposition nor erosion, the erosion that goes 
on at the shore line affecting only the emerging land. 
From the foregoing it appears that, while topset beds are not 
necessarily absent, they can be only very thin, and they will be 
largely removed by erosion as the shelf emerges. The bulk of the 
deposit forms foreset beds, and the material of these will be of 
somewhat coarse texture. 
