Figure 3. Gross geomorphic subdivisions of the Boston area (LaForge, 1932). 



Lowland, was re-eroded in part by glacial ice masses and subsequently 

 buried by glacial drift, alluvium, and coastal deposits. 



Since the bedrock surface under the Boston Lowland slopes generally 

 seaward, it probably lies deeper under the study area than on the adjacent 

 landmass. A few highs of the old topography outcrop on the sea floor and 

 form some of the islets in the near approaches to Boston Harbor. 



The two upland areas flanking the Boston Lowland to the north and south 

 are comprised chiefly of pre-Devonian igneous and metamorphic rocks with 

 some rocks of the Boston Bay Group. The bedrock surface is generally riot 

 as extensively or deeply buried in these areas as in the Boston Lowland. 

 Numerous bedrock exposures occur along the adjacent coast and appear as 

 rocky shoals, pinnacles, and islets in the coastal waters. Presumably the 

 northern and southern parts of the study area are also underlain by the 

 igneous and metamorphic bedrocks comprising the upland areas. 



c. Post-Paleozic Deposits . Although bedrock exposures occur through- 

 out the Boston area, most surficial and shallow subsurface deposits consist 

 of Quaternary glacial and glaciomarine sediments. Holocene fluvial and 

 marginal marine deposits are important locally along the coast and major 

 drainage ways . 



15 



