BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 6, pp. 343-352 APRIL 8, 1895 



DISCRIMINATION OF GLACIAL ACCUMULATION AND 



INVASION 



BY WARREN UPHAM 



{Bead before the Societ}/ December 2S, 1SD4) 

 CONTENTS 



Pago 



Ice-slicets and tlieir accumulation 343 



Views of others and of the author 343 



Thin margin and low gradients of the ice-sheets 344 



Erosion, transportation and deposition of drift by the ice-sheets 345 



Formation of moraines 345 



Local alpine or district ice-sheets and glaciers 340 



Probable causes of ice accumulation and departure. 340 



Ice accumulation attributed to high land elevation 340 



Ice departure attributed to land depression 347 



Invasion by the advancing border of an ice-sheet 347 



The advance not continuous 347 



Attendant drift erosion, transportation and deposition 348 



Displacement and folding of soft underlying beds 340 



Irregularity of glacial invasion and its meteorologic explanation 350 



Criteria of ice accumulation and invasion 351 



ICE-SHEKTS AND THEIR A('CUMULATION. 

 VIEWS OF OTHERS AND OF THE AUTHOR. 



In writing of tho history of the Ice age, the growth and culmination 

 of the ice-slieets, and their action in eroding, transporting and deposit- 

 ing the glacial drift, terms have l^een often used which imply or definitely 

 assert an advance, incursion or invasion by the l^order or somewhat steep 

 front of the ice, extending itself thus over new territory. In North 

 America, especially where the ice-covered area at the maximum stage 

 of glaciation wan about 4,000,000 square miles, the language of glacial- 

 ist** frequently brings before us a i)ictureof a thick ice-sheet amassed l)y 

 snowfall upon its central areas of outllow in Canada, as on the Lauren- 

 XLIX-HuLL. Geol. Soc. Am.. Vol. 0, 1891. (;{4;j) 



