POST-GLACIAL MARINE DEPOSITS 205 



the advance of the ice-sheet over this district. It may have been earlier 

 than or contemporaneous with the initial stages of the latest glacial 

 episode. 



Post-Glacial Marine Deposits 



Were the above elements of form and sculpture unsupported by evi- 

 dence of marine sediments, the case could be presented with no stronger 

 conclusion than a probability ; but there are such deposits, and they shed 

 additional light on the date of submergence. Two hundred yards south 

 by east from the summit of the knob there is a prominent outlying 

 ledge which is connected with the base of the knob by the long, sloping 

 profile of a wave-built bar (see plate 18, figure 1). Its uniformity is in- 

 terrupted by many ledges of rock in place, but between them, and par- 

 ticularly toward its lower end, the form of a bar is conspicuous. It is 

 composed of small pebbles, many of them thoroughly waterworn, and 

 the material on the whole resembles that of the occasional pebbly 

 beaches along the present coast. Gravel of similar character is to be 

 detected here and there throughout the pasture slope, but as it could 

 readily be explained as the wash of waters from the glacier, it would not 

 be significant were it not in the same locality built into the unmistaka- 

 ble submarine bar. In the material constituting this bar there are 

 striated stones clearly of glacial origin. 



On the northeastern side of the knob, at a point where converging 

 currents sweeping in from the south and southwest would meet in the 

 lee of the rock, there is a shoulder built of gravel at a maximum eleva- 

 tion of about 40 feet above the present sealevel, that is about 20 feet 

 below the old wave-cut bench. A pit, which has been excavated in this 

 bank (plate 18, figure 2), shows the gravels in section, locally exhibiting 

 steep cross-stratification in association with rather heterogenegus piling 

 of stones and sand. The stones are subangular and in some instances 

 striated. From among these stratified layers the writer picked out some 

 tiny fragments of shale, too small for determination and so decayed that 

 they crumbled with the slightest pressure. 



These scattered gravels occurring here and there upon the slope, the 

 wave-built spit connecting an outlying ledge with the summit, and the 

 embankment built below the old water-level in the lee of the rock, 

 appear to constitute a set of contemporaneous features, all indicative of 

 submergence during or following soon after the retreat of the ice. 



Summary 



Ames knob, a mass of uniformly hard andesite, exhibits a peculiar 

 bench, between 60 and 80 feet above the present sealevel, along the 



