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H. W. Shimer — Post- Glacial History of Boston. 4.37 



Art. XXXI. — Post-Glacial History of Boston; by H. "W". 



Shimer. 



Contents. 



Introduction. 



Typical section through the post- 

 glacial sediment of Boston. 

 List of species. 

 Conclusions. 

 Bibliography. 



Introduction. 



The recently completed excavations of the Boston Elevated 

 in the construction of the Boylston Street subway give many 

 new sections down through the mud to the glacial clay. The 

 resulting new exposures of the post-glacial shells through the 

 middle of Back Bay proved to be so interesting that it was 

 decided that a record of them should be kept. The following 

 is a brief summary of this work : 



Typical section through the post- Pleistocene sediment. 



The following section from the Boylston Street subway ex- 

 cavation at Exeter Street is typical of all the Back Bay sections, 

 and fairly so of all the others from Brookline to City Point. 



1. Fill, in blotting out the Back Bay 16 feet 



This fill has taken place mostly since 1868. 



2. Gravelly black silt. Few fossils 6 



3. Fine black silt. Many fossils 5 



The middle portion is very full of fossils ; the upper- 

 most two feet and the lowest foot contain but few. 

 This silt is a dark-gray (when dry) argillaceous sand 

 with a considerable number of mica scales. The 

 compound microscope shows that very minute sand 

 particles make up fully nine-tenths of the mass ; there 

 is merely sufficient clay and carbon particles to give 

 consistency and a dark-gray color to the sediment. 



4. Sandy, fresh-water peat 5 



5. Blue sandy clay with some peat 1 foot 



This is the upper edge of the glacial deposit. 



The surface of the street here is 16 - 5 feet above mean low 

 tide, while the bottom of the peat bed is 15'5 feet below mean 

 low tide. 



List of species. 



The following list includes all post-glacial fossils noted, or 

 listed by previous observers, from Brookline through Back Bay 

 to City Point. Appended to the list are notes upon the peat 

 and the oyster. 



