POST-GLACIAL HISTORY OF BOSTON. 



443 



northeast to Charles River. The generahzed section in this region 

 from above downwards is as follows * : — 



1. Alluvium, — 5 feet at the Longwood Bridge to 12 feet elsewhere. 



2. Peat, — averaging one-foot in thickness, containing stalks 



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o(K) 



Boston and vicinity in colonial time. The De Costa map, 1775, (reproduced 

 by permission of the Bostonian Society) forms the basis of the above sketch 

 map. The dotted parallel lines, exclusive of those showing Harvard (Tech- 

 nology) Bridge, indicate the dams built by the Boston and Roxbury mill 

 corporation. The numbers 1 to 7 refer to the sections described in this paper. 



of swamp plants, leaves of deciduous trees, and some shells, — 

 mostly iSIodiolus demissus var. plicatulus, embedded in some 

 sand and much mud. 

 3. Silt, — (no thickness given). Most of the shells noted in the 

 table below occur in this stratum immediately beneath the 



Arranged from Miss Bryant's thesis. 



