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M. L. FULLER — GEOLOGY OF FISHERS ISLAND 



At other localities, as at the Isabella Beach hill and the hill forming 

 the headland three-quarters of a mile to the northeast, the topography 

 is more puzzling, and only after the unraveling of the geology was it 

 determined that these hills were primarily constructional in form, repre- 

 senting in reality great anticlines in the Pleistocene sediments. 



Some of the depressions occupied by ponds are evidently true kettles, 

 representing the position of detached ice masses, which later become sur- 

 rounded or buried by glacial outwash, but other basins appear to be due 

 to the obstruction of older valleys by loose materials shoved up by the 

 last ice-sheet, or to the excavation of shallow basins by its erosive action. 

 Many of the more or less inclosed coves which occur along the coast of 

 the island represent similar features which have been partly submerged. 



The morainal topography is not confined to any one part of the island, 

 but is most marked along the north shore, where the knobs and kettles 



Figure 3. — Section through Hill Three-quarters of a Mile Northeast of eastern End of Isabella Beach. 

 Showing anticlinal structure of hill and the extent of marine erosion. 



are not only more conspicuously developed, but where erratic boulders 

 are present in the greatest numbers. On the south side, while morainal 

 features are not lacking, the topography commonly shows smoother and 

 more rounded outlines. The difference is evidently due to the fact that 

 the ice during the deposition of the morainal materials, which belong to 

 a retreated stage of the Wisconsin, reached in general only part way 

 across the island, the south shore topography showing to a greater or less 

 extent pre- Wisconsin forms slightly modified by the overriding ice dur- 

 ing the maximum advance when the ice margin stood at Block island or 

 beyond. 



Topographic forms due to wave action are of relatively slight impor- 

 tance. In general the bluffs are low, and erosion is only active in times 

 of especially severe storms. Usually they are covered by talus slopes, 

 which effectually mantle the outcropping strata. At Isabella beach and 

 again at the point three-quarters of a mile to the north the bluffs are 

 steep and clean. The exposure at the latter point is of special interest, 



