86 Kansas Academy of Science. 



• SUMMARY OF GLACIAL LITERATURE RELATING TO 

 GLACIAL DEPOSITS. 



By Albert B. Reagan, La Push, Wash. 

 GLACIAL DRIFT. 



Definition. — "Glacial drift is an accumulation of earthy materials — 

 clay, sand, gravel, and boulders — which has been transported by moving 

 masses of ice and deposited over portions of the earth's surface, mostly in 

 the higher latitudes." — Standard Dictionary. 



"This aggregation of surface material which overlies different for- 

 mations indiscriminately, and which is composed of materials which 

 could not have been derived wholly from the underlying rock, is called 

 drift." — Rollen B. Salisbury. 



GENETIC CLASSIFICATION. 



13ASED upon the origin of their formation, glacial deposits 

 -*^ are classed as subglacial, englacial, superglacial, and ex- 

 traglacial. 



SUBGLACIAL DEPOSITS. 



The subglacial deposits are those deposits which are 

 dragged along beneath the ice or are formed beneath the ice. 

 They are: Lower till, ground-moraine, or boulder-clay. This 

 is the "hard-pan" clay formation found throughout glaciated 

 regions. It is sometimes called boulder-clay because it con- 

 tains boulders and pebbles. It is the product of abrasion 

 caused by the stones held in the moving ice-sheet grinding 

 the bed-rock into powder, and the bed-rock, in turn, reducing 

 them to the same material. When the great ice-sheet melted 

 its load was dropped, and in this deposit the coarser and finer 

 materials beneath the sheet were indiscriminately mixed ; thus 

 the till or rock-flour. 



An examination of this till in Wisconsin gave the following 

 results : It is of medium hardness when dry and slakes read- 

 ily in water, breaking down into a finely pulverulent mass 

 which has a fair degree of hardness. Under the microscope 

 the grains were observed to have diameters ranging from 10 

 mm. to 0.003 mm. A very small percentage of the individuals 

 are less than 0.0058 mm. in diameter. The larger grains are 

 fairly well rounded, but the smaller ones have angular out- 

 lines. 



To use the Standard Dictionary definition for this forma- 

 tion, it is "an accumulation of earthy materials — clay, sand. 



