536 THE JOURNAL OF GEOLOGY. 



next the impounding ice. Practically, this characteristic is not 

 always readily demonstrable. 



3. By bordering s?as. 



This class differs from the preceding in the fact that the 

 waters were not impounded by the ice (as they usually, but not 

 always, were in the preceding case), and in the fact that the 

 deposits are commingled with oceanic sediments, marine fossils, 

 and impregnated with saline waters, which may or may not have 

 been wholly removed subsequently. 



IV. Formations produced by floating ice derived from Pleistocene 

 glaciers. 



The type of this class is glacio-natant till, in which the con- 

 stituents are identical with those of glacial till except when 

 formed under the action of currents which induced secondary 

 modifications. Two sub-classes are to be recognized : 



1. Local. — In general these are lacustrine but may be oceanic. 

 Commonly the deposits took place in glacier-fringing (usually 

 glacier-formed) lakes and constitute only a secondary phase of 

 glacier formation. In cases in which the ice entered an arm or 

 bay, or even the border of the ocean, and the deposit took place 

 in the immediate vicinity, the deposit remained essentially a local 

 one. If marine fossils or marine sediments were commingled, or 

 if the marine factor is for any reason regarded as important, a 

 sub-classification distinguishing between lacustrine and marine 

 glacio-natant local deposits is justified. 



2. Foreign. — These are essentially marine glacio-natant 

 deposits and are due to icebergs derived from distant glaciers 

 bearing to the point of deposit material wholly of foreign origin. 

 Among the genetic conditions involved in this case are the sub- 

 mergence of the land beneath the ocean at the time of the 

 deposit and its subsequent elevation. Local lacustrine glacio- 

 natant deposits may be formed at various heights above the 

 ocean level and subsequently exposed by the drainage of the 

 lake without involving oscillations of the crust or the sea level. 

 In the case of the great lakes, iceberg material borne from one 



