The Charles River in Massachusetts.—Clap p. 229 
to correspond closely with those derived from the most prob- 
able development of the Tertiary drainage. 
Glacial Lake Charles. 
At the beginning of the Pleistocene period occurred the 
great elevation of the land which ushered in the Ice age. With 
the subsidence at the close of the Ice age, came the melting of 
the ice-sheet and the release of great volumes of water, which 
collected south of the receding ice-front in northward sloping 
valleys to form glacial lakes. In basins where the preglacial 
drainage had been to the north, the water-parting on the south 
naturally formed the southern barrier of the glacial lake. But 
in the basins of the upper and middle Charles the greater part 
of the preglacial drainage was southward. In these cases, at 
times when the ice-front rested at narrow portions of the south- 
sloping valleys, the detritus-laden streams from the ice-sheet 
formed apron-plains of sand and gravel which completely 
closed the valleys and presented an effectual southern barrier 
to the glacial waters. . 
Lake Charles, being retained on the south by the frontal 
plains and the intervening highlands, and on the north by the 
high ice-front, necessarily overflowed through the lowest pass 
in its southern water-parting. As the ice receded northward, 
lower and lower passes were uncovered in the southern and 
eastern sides of the basin, serving as successive outlets for the 
lake, and allowing the water to fall each time to a lower level. 
Each stage of the lake is characterized by extensive deposits of 
modified drift, the maximum elevation of each coinciding ap- 
proximately with the level of the lake during that stage. 
Bellingham and Wrentham Stages.—During its history 
lake Charles had twelve distinct outlets, two of which coin- 
cided with outlets of glacial lake Neponset (plate 16). The 
stages are less in number than the outlets, however, for dur- 
ing the earlier history of the lake each stage had several out- 
lets at or near the same level. Thus the two outlets in the 
vicinity of Bellingham and those southeast of Franklin have 
all an elevation of about 240 to 260 feet. The stage of the 
lake corresponding with these outlets may be called the Bel- 
lingham stage. 
Simultaneously with this was the Wrentham stage, dur- 
ing which the ice was disappearing from the region east of 
