9 

 POST-GLACIAL HISTORY OF BOSTON. 447 



inches. Taking Mr. L. S. Stone's estimate of the greater length 

 of seven feet, there would he from six to se\en feet of silt above the 

 sticks. For a consideration of their age there must be added to 

 this the thickness deposited between the driving of the sticks and the 

 deposition of sediment o\er their decaying ends. The wood testifies 

 to its great age in being exceedingly brittle and very heavy, showing 

 that a certain amount of petrifaction had occurred. Its \ery dark, 

 almost black, color indicates, likewise, considerable carbonization. 



f. Arlington Street. 



Feet 



1. Fiir 16 



2. Black silt 5 



A few shells are reported from near the top of this. 



3. Boulder clay 17 



The boulders are well rounded, and are more numerous at 

 the bottom of the section, w^here they make up fully one-half 

 of the sediment. The boulders are usually two to three 

 inches in diameter; the largest noted had a diameter of three 

 feet, with corners all well rounded. This clay was not pene- 

 trated farther up Boylston Street. 



g. Church Street. At some thirty feet below the surface of the 

 street (which is here fifteen feet above low tide) a tree stump was 

 excavated from near the top of a peat bed. The peat continued 

 eighteen feet below the stump. The stump was reported as uncar- 

 bonized. Apparently another tree was encountered in a wash-boring 

 near here. 



h. Charles Street. At the Public Garden side of Charles and 

 Boylston streets a boring penetrated a peat bed 27.5 feet thick. 

 The bottom of the peat is 42 feet below the surface of the street, 

 which is here 15 feet above low tide. 



5. Site of Old Providence Depot. The following were found 

 while excavating Providence Street:* 



Mya arenaria r. Small 

 Ilyanassa obsoleta C. 

 Littorina rudis r. 



6. Commonwealth Flats, South Boston. Peat was en- 

 countered here 20 feet below low tide.f 



* Collected by Mr. E. L. Green. 



t Communicated by Mr. R. W. Sayles. 



