ESKERS IN THE VICINITY OF ROCHESTER, NEW YORK. 167 



till, or from a swampy area of thin till. They exhibit a tendency lo 

 originate in places favorable to a large accumulation of water, as 

 level plains, broad basins, and near the top of low divides. They 

 may arise from the lee end of a drumlin. 



Character of course. The course, as already indicated, pursues 

 commonly a sinuous direction ; rarely is an esker straight for any 

 distance. It meanders, the long deflections, sometimes a mile or 

 several miles in length, appear to obey the topography, the short 

 deflections, only a few feet to a fraction of a mile long, resemble 

 stream meanders. Fvirther, esker courses are unsymmetrical, 

 abrupt tvu'ns and sharp angles being a not uncommon feature. 

 ^Maxima changes in the course may be accompanied by maxima 

 changes in the elevation of the crest line (122). 



The crest may remain as narrow as a wagon road, again it may 

 spread out into terrace-like flats, in conformity with a similar 

 increase in the breadth of the base, and become higher than the rest 

 of the esker. In the case of the eskers of the interior these flat 

 areas are rarely more than 500 feet wide, in the case of the Maine 

 eskers they may be exceptionally a mile or more in width. These 

 broad "plains" may contain kettle holes, variously known as basins, 

 sinks, funnels, hoppers, punch bowls, and Roman theaters (99). 

 These kettles may be as deep as the esker is high, and may contain 

 water indicating an impervious bottom. These broad places may 

 show evidences of stream erosion, and boiling springs may occur 

 along their flanks. 



The esker ridge may divide, and two parallel ridges may unite 

 to form one ridge. The main ridge may break up to form several 

 distributary ridges, every one of which exhibits the same height and 

 width as the main ridge. These distributary ridges may interlace 

 complexly, enclosing numerous kettle holes, which may have outlets : 

 again they may contain water, and may be floored with till. Such 

 a system of meandering and anastomosing ridges may be connected 

 by lateral and transverse branches enclosing large areas of the coun- 

 try. The width of such complexes may be as great as 5 miles, and 

 the length 10 to 20 miles, the whole often representing a jumble of 

 heaps, mounds, cones and ridges. Such reticulated eskers find their 

 best development in this country in southwest ]\Iaine. where they lie 



