ANCIENT WATER LEVELS OP CHAMPLAIN-HUDSON VALLEYS 205 



such power as did the waves at the 330 foot level or if they had 

 this strength they acted for a much shorter time at each level. 

 It is to he presumed, when the mouths of the Ghamplain and 

 the St Lawrence valleys were freed from the ice sheet, that 

 the winds from the north and east would have had a greater 

 fetch and that the glacial lake conditions of the higher water 

 levels would be at once exchanged for more vigorous cliff cut- 

 ting. It has therefore seemed to me highly probable that this 

 cliff has its base approximately at the marine limit. There is 

 another consideration which supports this view. 



It is to be shown presently that the marine limit of this epoch 

 is now tilted more steeply to the south than the shore lines of 

 the earlier water-levels on the south. It appears to follow 

 fronuthe divergence of these ancient water planes, that before 

 the marine invasion was established, the land was tilted down 

 toward the north, thus determining the extent of the submer- 

 gence; since then the land has risen. The marine action would 

 undoubtedly be longer maintained at the level of the maximum 

 of depression of the shore lines, for there the sinking land 

 halted, reversed its movement and came up. Thus we ought to 

 find, other opportunities being equal, rather decided evidences 

 of wave action at this particular water level, for the land probably 

 stood longer at the marine limit than at any other stage in its 

 movement. 



On the basal slopes of Trembleau mountain to the east of 

 the cliff, are patches of beaches with well waterworn pebbles 

 between the bare ledges at about the level of the base of the 

 cliff above described. 



There is also a very extensive development of the gravelly 

 and sandy delta of the Ausable just below this level indicative 

 of a longer stage of delta building than is found again below this 

 level. If I am not mistaken Mr S. P. Baldwin has taken this 

 delta to mean the same thing — the local index of the marine limit. 



True proportions of the postglacial tilting of the upper marine 

 lint it. Lest the reader obtain from the diagrammatic profile of 

 plate 28 an exaggerated idea of the steepness of the tilting of 

 the old sea level in the Champlain valley, let him construct a 

 straight line 1 mm thick having a length of 1196 mm. The thick- 

 ness of this line will have the same proportion to the hight of 



