THE LOESS. 417 



the forces maintaining the present contour of the earth's sur- 

 face may be very evenly balanced, so that a slight addition 

 at one point, and subtraction from another, might be the de- 

 cisive influence in turning the scale. It is now pretty gener- 

 ally believed that the long-continued and steady periods of 

 subsidence involved in the formation of extensive sediment- 

 ary rocks was due to the constant accumulation of the silt, 

 out of which the rocks are made. This silt was relieving the 

 continents of its weight, and adding to the weight along the 

 whole line of deposition. During the Glacial period the 

 transference of water from the ocean to accumulate as ice 

 upon land removed an immense pressure from the ocean- 

 beds, and added an equal amount of weight to the glaciated 

 area. How much influence this may have had in depressing 

 temporarily this area and its margin, we are unable to tell. 

 But it is one of those unknown causes in the field which may 

 be supposed to have accomplished something. 



Professor Alexander Winchell has, in a recent interesting 

 paper, suggested a correlation between this pressure of the ice 

 over the glaciated region and the enormous outflows of lava 

 along the Rocky Mountains and the Cascade Range on the 

 Pacific slope.* The lava-beds of that region are enormous in 

 extent and are certainly of very recent date, and seem to 

 have poured out from long fissures instead of craters. Under- 

 neath these beds there are, in California and Oregon, glacial 

 deposits ; and it is in these lava-covered glacial deposits of 

 southern California that human remains are supposed by 

 Whitney to have been found. Professor Winchell's theory 

 connecting those lava outflows with the depression produced 

 by the ice of the Glacial period in the east would relieve 

 the subject of considerable embarrassment arising from the 

 chronological difficulties that have been suggested. To the 

 superficial objection that pressure over the Mississippi Valley 

 would not produce volcanic eruptions at so great a distance 



* " Some Effect of Pressure of a Continental Glacier," in " The American 

 Geologist,'' March, 1888, pp. 139-143. 



