PLEISTOCENE GEOLOGY OF NASSAU CO. AND BOROrGH OF QUEENS 665 



Cone. Conical pile of rudely stratified sand and gravel often with included 

 boulders with a fan-shaped outward base, and a steep face toward the posi- 

 tion formerly held by the ice front against which it was deposited by out- 

 pouring, waste-laden water from the melting ice 



Crease. One of the channels formerl}- held by a stream coursing over the surface 

 of a delta or glacial sand plain and now usually dry for the reason that the 

 water came from the melting ice along the front of which the deposit was built 



Cuesta. In physical geography, a land form consisting of a perceptibly inclined 

 plain overlooking a steep slope or escarpment on its higher side, developed 

 by erosion on the retreating outcrop edge of a gently inclined hard stratum 



Digitation. Fingerlike branching of the headwater tributaries of streams 



Drift. See Glacial drift 



Drumlin. Lenticular or oval, drum-shaped hill composed of till deposited by 

 an ice sheet; distinguished from a kame by its usually greater size, its elon- 

 gate oval form, and its composition 



Drumlinoid. Having the form of a drumlin 



Esker. Long winding ridge of gravel and sand, often associated with glacial 

 sand plains and kames, and considered by most geologists to be the deposit 

 made in the channel of a subglacial stream 



Esker-fan. Small glacial sand plain or delta with a lobate outward margin and a 

 terrace, often cuspate, on the inward margin facing the ice sheet against which 

 it was formed at the same time that the associated esker was being deposited 

 inside the ice sheet 



Fore-set beds. Cross bedding often on a large scale developed in formation of 

 the subaqueous portion of deltas. Each fore-set bed is an underwater talus 

 formed at the growing edge of the delta where the stream coursing over the 

 surface of the delta drops its load on reaching open water. The beds incline 

 steeply forward in the direction in which the delta is building, hence the 

 name. Fore-set beds are usually overlain by the top -set beds, which see 



Fosse. Depression or unfilled area often found between the terraced ice contact 

 of glacial sand plains and morainal mounds forming a belt within the ice 

 covered field, as on Nantucket 



Glacial drift. In a general sense, the boulders, till, gravels, sands and clays 

 transported by glaciers or the stream flowing from them; specifically in some 

 writings, unstratified or ice-laid drift. Unmodified, unstratified, or unassorted 

 drift are expressions referring to the till or ice-laid drift; modified, stratified, 

 or assorted drift are expressions applied to the water-laid gravels, sands, and 

 clays produced in the vicinity of melting glaciers or remnant masses of ice 



Glacial lobe. One of the lobate protrusions of the margin of an ice sheet, some- 

 times a score or more miles in width as where the ice has been free to spread 

 out in depressions along its margin 



Glacial retreat. A glacier is said to retreat when its front recedes. The ice may 

 be actually moving forward toward this front, but the rate of backward melt- 

 ing at the front, if it exceeds the rate of forward movement, will cause the 

 position of the front to recede 



