82 BULLETIN OF THE ESSEX INSTITUTE. 



kettle-holes and frequently are the sites of large glacial 

 lakes. Depressions of this class are typical ice- block 

 holes. 



A drainasre crease sometimes starts from the ice-block 

 hole and traverses the plain ; such furrows do not origi- 

 nate in kettle-holes as defined in this paper. In the 

 kettle-hole the ice did not rise above plain level ; in the 

 ice-block hole, the ice once rose above plain level and 

 the drainage ran across the plain. 



Imperfect ice-block holes sometimes occur in the margin 

 of wash-plains as between the lobes of the Drownville 

 delta in Rhode Island. A similar phenomenon has been 

 reported by Fairchild in western New York. 



Large ice-block holes surrounded by the ice-contact are 

 to be distinguished from " unfilled areas " between suc- 

 cessive retreatal plains. Such unfilled areas will exhibit 

 the ice-contact about their southern margins and lobate 

 delta fronts about their northern border where later plain 

 building has carried sands into the depression. 



From the point of view of glacial geology, the occur- 

 rence of lakes in ice-block holes is an accident dependent 

 on the height of the water-plane in the surrounding 

 gravels. There are many ice-block holes of large size 

 without lakes. Such depressions exist in the Plymouth 

 area. 



Ice-block holes are sometimes grouped, as where in the 

 bottom of a large depression there are two or three isolated 

 deep holes. The accompanying map (fig. 2) of the Aga- 

 wam river area in Plymouth County, Mass., shows an 

 example of this mode of occurrence. In this case the 

 holes are occupied by water. 



Typical ice-block holes in this region seldom, if ever, 

 show ravines caused by streams eating back into the sur- 

 rounding terrace. Kettle-holes, on the contrary, as in 



