186 ROCHESTER ACADEMY OF SCIEXCE. 



many new channels, particularly on long gentle slopes where this 

 type is apt to occur. "In this way large numbers of narrow chan- 

 nels were formed, connected at frequent intervals with one another 

 by transverse channels". (Stone). They may represent ridges 

 formed where streams debouched into open standing water from the 

 ice front (97). Here they would be comparable to the distribu- 

 taries of modern deltas, enclosing basins, kettles, etc. Lacustrine 

 deltas formed in glacial lakes have been observed to be more or less 

 reticulated toward their landward extremity. This feature may also 

 have been formed as a lacustrine delta in a local enlargement of a 

 subglacial stream, possibly roofless. Every stream flowing into the 

 lake would build its lateral ridges, kettles would be enclosed by these 

 growing ridges, and ice block inclusion would form others. On the 

 north side of divides uncovered by ice ablation lakes might form and 

 its numerous more or less connected subglacial tributaries northward 

 give rise to reticulated ridges. As a result of clogged subglacial 

 chan;iels, the water might become superglacial and the resulting 

 superglacial deposits become a jumble of ridges, cones and hollows 

 on the melting of the ice beneath, these would constitute a narrow 

 area of reticulation. They also may have been formed in an exces- 

 sively crevassed ice front not bathed in glacial lake waters. Such 

 crevasses might be produced by tension. 



Ice movement probably destroyed eskers. Their almost uni- 

 versal absence from the glaciated interior and from other glaciated 

 regions, with possibly here and there an isolated occurrence, except 

 in especially favored localities such as ]\Iaine, may be explained not 

 so much from lack of deposition in subglacial channels, or absence 

 of subglacial drainage, but by the fact that subsequent or persistent 

 ice movement destroyed the majority of those already formed. Ice 

 advance might destroy eskers already uncovered by ice retreat as 

 well as those formed or partially formed still beneath the ice. Vigor- 

 ous drainage at the ice front may also have been a contributing factor 

 in esker destruction as soon as they were uncovered. Stone explains 

 the absence of glacial gravels near the coast of Maine as a result of 

 "a small acceleration in the ice flow near the coast and limited en- 

 largement of the subglacial tunnels over the area whose basal ice was 

 submerged in the sea" (99). Eskers may have been destroyed as a 

 result of subsequent erosion by the same stream that built them. 



