114 W. TJjpham — Epeirogenic Movements 



Art. XYI. — Epeirogenic Movements associated with Glacia- 

 Hon; by Warren Upham. 



Geology is indebted to Gilbert in his monograph, " Lake 

 Bonneville," for the terms ejpeirogeny and epeirogenic, desig- 

 nating the broad movements of uplift and subsidence which 

 affect the whole or large portions of continental areas or of the 

 oceanic basins. These terms are distinguished from orogeny 

 and otogenic, which denote the folding, faulting, and upheaval 

 of limited tracts as mountains and mountain ranges, forming 

 narrow belts as compared with the extensive plateaus of the 

 continents. Epeirogenic uplifts and depressions, except in 

 areas of contemporaneous orogenic disturbance, take • place 

 apparently by gentle monoclinal or quaquaversal tilting of the 

 marginal or outer parts of the broad regions affected, and 

 exhibit a very gradual change in altitude from the central 

 parts of those regions to the undisturbed surrounding areas. 

 In the region of Lake Agassiz and of the Laurentian lakes, 

 whose epeirogenic elevation after the recession of the ice-sheet 

 has been well ascertained in its southern part by levelling and 

 is found to vary from a few inches to somewhat more than 

 five feet per mile of differential uplift from south to north, 

 the movement has been so gradual that the continuity of the 

 glacial lake beaches remains perfect, with no dislocations to 

 indicate any faulting of the underlying bed-rocks. 



Especial interest pertains to the epeirogenic movements of 

 the Quaternary era from their relationship to the accumulation 

 and departure of the Pleistocene ice-sheets, which was first 

 pointed out by Dana in his presidential address before the 

 American Association in 1855, as published in this Journal the 

 following year. By reasoning from the prevalence of fjords 

 in all glaciated regions and showing that these are valleys 

 eroded by streams during a formerly greater elevation of the 

 land previous to glaciation, and from the marine beds of the 

 St. Lawrence valley and basin of Lake Champlain belonging 

 to the time immediately following the glaciation, it was an- 

 nounced that the formation of the drift on this continent was 

 attended by three great continental movements : the first up- 

 ward, during which the ice-sheet was accumulated on the land ; 

 the second downward when the ice-sheet was melted away, and 

 the third, within recent time, a re-elevation, bringing the land 

 to its present height. With the moderate depths of the fjords 

 and submarine valleys then known, the amount of preglacial 

 elevation which could be thus affirmed was evidently too little 

 to be an adequate cause for the cold and snowy climate pro- 



