SUBMERGENCE PHENOMENA 609 



E. S. Tarr described gravel bars 40 to 60 feet above the sea. In tlii 

 supplementary note Woodworth raised the figures to 80 feet. Tarr also 

 described and figured contorted sand beds at Gloucester containing 

 marine fossils and large boulders, and says: 



"The clayey layers also suggest a subsidence sufficient to remove the area 

 from the immediate neighborhood of the rocky coast; and the presence of 

 boulders, some of which are fully two tons in weight, suggest sufficient depth 

 for large masses of ice to float. It seems difficult to account for these trans- 

 ported fragments in water having a depth less than a hundred feet" (71, page 

 191). 



Our map, figure 2, makes the submergence at Cape Ann about 350 feet. 

 The disturbance of the sands might be due to icebergs, and the over- 

 lying till is probably berg till. 



1,. SAyDPLAINS OF INFERIOR LEVELS 



Wave-smoothed and more or less leveled plains occur at all levels, 

 from the summit marine plain down to the present sealevel, and they 

 are regarded as the proof of the slow rise of the land out of its sub- 

 mergence. These plains are not limited to valleys or hollows or embay- 

 ments of the land, and glacial waters are too ephemeral and too spas- 

 modic to produce such vertical series of plains. The ^ewtonville sand- 

 plain and the many smoothed tracts in the same district, noted by Clapp 

 (68), are examples of this class of abundant features (see page 604). 



For reasons given above, it is believed that the inferior plains could 

 not have been built as outwash plains in contact with the ice-front and 

 at the water level, although when deposited as kame or pell-mell gTaveis 

 in deep water the deposits were commonly banked against the ice-front. 

 Some of the form due to the ice contact may be preserved during the 

 later process of wave-leveling. As these level sand areas have been 

 interpreted as outwash plains at water level, or glacial deltas, it is 

 desirable to note some of the discriminating criteria. 



True constructional plains should exhibit delta form and structure, 

 as clearly set forth by Davis in 1890 (40). By contrast, the wave- 

 leveled or erosional plains, due to smoothing of kames or deep-water 

 deposits, should lack most of the delta characters. They should be more 

 nearly level, and any surface slope should decline away from the side 

 of wind exposure and heavy wave-work, and would commonly be in 

 opposite direction from the glacial outflow; or, the declining slope may 

 be radial from the original knolls or locus of supply. The gradation iv 

 size of the surface materials should tend to have the same relationship 



