444 SHIMER. 



peat bed, crowded thickly together. The shells range almost 



to the Boston and Albany Railroad station in Brookline; 



there are none to the southwest of this. 



4. Eroded sand plain (a glacial deposit). At the Longwood 



Bridge the sand plain had been eroded to a depth of 37 feet 



before the deposition of the five feet of alluvium. 



2. Charles River, directly east of the Harvard (Technology) 

 Bridge extending between Back Bay and Cambridge. During the 

 dredging here to fill in the shallows on the Cambridge side between 

 the newly constructed wall along the river and the railroad tracks, 

 many shells were found. These shells occurred mostly in the sands 

 and not in the superficial muds. These sands were some ten feet 

 below mean low tide. The height of the tide here, before its oblitera- 

 tion by the dam, was ten feet. 



The most conspicuous species are the large and abundant forms 

 of oyster (Ostrea virginica), short-neck clam (Venus mercenaria), 

 long-neck clam (Mya arenaria) and scallop (Pecten gibbus borealis). 

 A small oyster shell is unusual, the average size being 8 by 2.5 inches; 

 one figured by Miss Bryant had a length of 10.5 inches. 



During early colonial days (middle of the seventeenth century) 

 an extensive oyster-bank existed here, preventing large boats from 

 going farther up the Charles. (See p. 451). 



3. New Tech Site. The new site for the Massachusetts Institute 

 of Technology occupies the northeastern angle between Charles 

 River and Massachusetts Avenue. The many bore-holes put down 

 here while the foundations of the new buildings were being planned 

 showed that the solid rock bottom varied much in depth. The follow- 

 ing is one of the deeper sections, — 



1. Fine and coarse sand, much of it colored green ; 35 feet. Uniden- 



tifiable fragments of fossils were present in the material brought 

 up by the wash-drill. 



2. Soft to stiff blue clay (a glacial deposit) ; 83 feet. 



3. Decomposed bed-rock of slate; 14 feet. The boring stopped 



in the slate at a deptli of 132 feet. 



4. Boylston Street Subway localities. The sections were made 

 at or very near the junction with the following streets: 



a. Fairfield Street. The top of the peat is 18 feet below mean 

 low tide; the peat is 5 feet thick. 



