346 Geology of Portland. 



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direction in which these islands were seen^ when the 

 sketch was taken, was Southerly. 



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Geological Changes produced ly Molluscous Animals. 



I have been much interested in some observations and 

 facts communicated to me recently by Dr, James E, De 

 Kay, now resident at Oyster Bay, Queen's county, Long 

 Island. And I take the liberty to give them in his own 

 language, presuming that Dr. De Kay will pardon such 

 a use of a private letter. 



*^ I have resided latterly/' says he, " on the shore of a 

 large bay, on the northern coast of Long Island; and the 

 changes effected on its sandy beach by winds, tides, and 

 apparently irregular currents, have attracted much of my 

 attention. It has, however, often been a matter of great 

 difficulty to account for the deposition of materials in 

 places, where, from the operation of the above named 

 causes, they certainly ought not to be foundi Will the 

 following facts throw any light on this subject ? 



" In a calm, still day, I have frequently noticed the 

 surface of the water covered with patches of sandj vary- 

 ing in extent from one to six or eight inches square. 

 These patches are composed, of course, only of the finer 

 portions of sand, adhering to each other by a thin film of 

 gelatinous matter, which gives buoyancy to the mass. I 

 have been surrounded frequently, by patches of this kind, 

 in tolerably close contact, and covering a surface of several 

 hundred acres. The lightest touch of an oar, or a slight 

 breeze, causes them to sink immediately. The rationale 

 of their formation I conceive to be this. The shore we 

 know to be peopled with myriads of minute raollusca, 

 furnishing, either by their excretions, or their own proper 

 bodies, a gelatinous substance, which hardens unon ex- 



