PROOFS OF SUBMERGENCE 295 



The inner (northern) border of the siibaqneoiis plain, next to the sub- 

 aerial oiitwash; is remarkably smooth and flat. Here the channels of the 

 oiitwash mostly disappear, and the depressions or hollows which do occur 

 are usually without definite limits and lack the characters of stream 

 channels. The surfaces are as flat and smooth as could be expected on a 

 sandy tract steadily lifted out of shallow Avaters. 



In the eastern part of the island some extensive areas, like that be- 

 tween Eiverhead and Mattitnck, are perfectly level, unbi'oken plains 

 except for the kettle basins. These basin features will be considered 

 later. 



SVRFICIAL LOAMS 



Some facts connected with the surface soils and composition of the 

 plain are inconsistent with the theory of subaerial origin. The occurrence 

 of loamy surface soils over considerable areas, giving good farm lands for 

 general agriculture, was long ago recognized. Watson Avrote (2) : 



"There prevails the same superficial loam, from one to three feet deep ; then 

 succeeds small gravel mingled with the loam, which rests on the unifoini 

 foundation of coarse and rounded gravel" (page 494). 



If the plain had been wholly built by glacial outwash in the open air, 

 the flner detritus would have remained in the grasp of the storm wash 

 and streams until dropped in relatively quiet standing water. The fact 

 that such fine material now forms a veneer over large areas proves that 

 these areas were under water. Erosion in the shallow water and in the 

 air has removed the veneer of silts along the lines of flow, so that the 

 depressions and channels show sand and gravel. Watson wrote : 



". . . and it is a singular circumstance, which marks the anomalous ar- 

 rangement of the whole island, that unlike every other territory the soil is 

 thinnest and least fertile in depressions than on the elevated parts of the 

 surface" (page 487). 



"The greatest thinness and barrenness of soil occurs in the depressions, 

 while the best and heaviest land is found on the elevated parts of the plain. 

 . . . Ravines running north and south traverse, at intervals, the plains, and 

 these, uniformly, have the lightest and thinnest soil" (page 495). 



It is possible that Watson confused in some cases the exposures of stiff 

 brick clay of preglacial or interglacial origin which underlies the glacial 

 outwash and in the moraines is pushed up in masses and involved with 

 the till; but, making allowance for this and for his rather sweeping 

 statements, it is yet true that he properly emphasized the loamy character 

 of much of the plain. 



Another interesting fact is the absence of stones over most of the 

 southern plain. On large areas scarcely a pebble can be found. 



XXI — BuLi.. Gkol. Soc. Am., Vol. 28, 1916 



