312 MYRON L. FULLER 



this southern belt that the writer first encountered exposures of 

 till of a type entirely unlike that ordinarily prevailing over this 

 part of New England. In composition, in color, and in weathering, 

 the till in question was strikingly different from the ordinary buff 

 till of the region, and had the aspect of being much older than 

 the latter. A further study of its character and associations was 

 found to corroborate the differences first noted, and apparently 

 warranted the conclusion that it should be considered as repre- 

 senting the deposits of an ice sheet which certainly antedated 

 the last invasion, and probably marked the earliest of the Pleis- 

 tocene advances. 



The area embracing these tills is located in the eastern and 

 central portions of the Dedham quadrangle of the United States 

 geological survey at a distance of some twenty miles south of 

 the city of Boston. The position of the quadrangle and of the 

 area of tfye till localities is shown in Fig. I. 



It will be seen from this map that the tills are situated some 

 fifteen to twenty miles inside of the interlobate moraine near 

 Plymouth, and at a distance of some fifty miles north of the line 

 of the corresponding terminal moraine. This moraine, for in 

 origin it is a unit, is usually correlated chronologically with the 

 Wisconsin. If this is so, and there are apparently no grounds 

 for doubting the conclusion, it is evident that the till sheet 

 which covers the surface of this portion of Massachusetts to an 

 average depth of perhaps five to fifteen feet, and which is clearly 

 contemporaneous with the moraine, is likewise of Wisconsin age. 



Observations on Massachusetts glacial deposits of an age 

 earlier than those of the last ice advance have been few in num- 

 ber and, with the exception of occasional instances of the burial 

 of stratified drift deposits beneath later tills, have been confined 

 to the vicinity of the moraines along the south coast where the 

 conditions for differentiating the glacial deposits are more favor- 

 able than in the inland area to the north. 



Before considering the evidences of older tills which the 

 writer believes he has discovered beneath the Wisconsin till 

 sheet, mention will be made of a number of papers presenting 



