POST-GLACIAL HISTORY OF BOSTON. 451 



with a length of 140 mm. has a maximum thickness of 50 mm. At 

 City Point the specimens are similar in size and abundance to those 

 from Charles River. Miss Bryant figures one from here 265 mm. by 

 80 mm. 



This oyster, as native, is now absent from Massachusetts Bay; 

 during early colonial days it occurred only locally and then, on account 

 of the cold air at such depths as to be exposed only at the low spring 

 tides. A large oyster-bank was situated at the mouth of the Charles 

 River, another at the mouth of the Mystic and probably one on the 

 Noddles Island, now East Boston, fiats. 



That the large current forms flourished in Back Bay as late as the 

 middle of the se^■enteenth century is shown by the following quota- 

 tions (5): 



"The Oisters be great ones in forme of a shoo home, some be a 

 foote long, these breed on certain bankes that are bare every spring 

 tide. This fish without the shell is so big that it must admit of a 

 division before you can well get it into your mouth.". . . ."Towards 

 the southwest in the middle of this Bay" (i. e.. Back Bay, at mouth 

 of Charles River) " is a great Oyster-banke " ..." The Oyster-bankes " 

 (referring to the same) "doe barre out the bigger ships." 



In the first edition (1841) of the " Invertebrata of Massachusetts," 

 Dr. Gould says (p. 357) " old men relate that they were accustomed 

 to go up Mystic River and Charles River, and gather oysters of great 

 size, before it was the custom to bring them from New York. And 

 even now individuals of enormous size are occasionally brought from 

 both these places, and probably might be found by special search, at 

 any time." 



The cause of this great numerical reduction since colonial days 

 is said to be a very severe cold spell about 1780 in which the sea 

 bottom was covered with ice, thus preventing the oysters from getting 

 air. Another factor which aided in the destruction of some of these 

 species, especially the oyster, from the Back Bay region was the 

 gradual obliteration of Boston as an island by the formation of a neck 

 uniting it with the mainland to the south. Even during late colonial 

 days heavy seas washed over this neck into the Back Bay. Oysters 

 need a clean substratum, such as gravel, or other shells, to which 

 the young, the spat, may attach themselves, otherwise they will 

 perish; and the opening across Boston neck would give the tidal 

 currents extra strength with which to cleanse this partially enclosed 

 region from the river muds; but that this was never so exposed to the 

 action of waves as at City Point is shown by the occurrence of the 

 surf-clam (Mactra solidissima) at the latter place only. 



