G. F. Wright— Unity 'of the Glacial Epoch. 361 



forest beds on its way. These inferences have been fully con- 

 firmed by the investigations of Professors Reid and dishing 

 who spent the summer of 1890, on the same ground (see Na- 

 tional Geographic Magazine for March, 1892, and The Ameri- 

 can Geologist for Oct., 1891). Indeed Professor Reid's photo- 

 graphs show that the ice front had receded 3,000 feet during 

 the four years intervening between our visits and he is con- 

 fident that the glacier has receded fourteen miles during the 

 century. These observations reveal also unexpected rapidity 

 in the movements of great glaciers and remarkable capacity of 

 ice in certain conditions to creep over unsolidified strata of 

 sand and gravel without disturbing them. From the rapidity 

 with which both forests and ocean fauna follow up a retreat- 

 ing ice front where, as in this case, it debouches into an arm 

 of the sea, it is clear that two or three centuries are sufficient 

 to produce a forest bed of considerable extent with all its 

 accompaniments of glacial deposits below and above. 



In addition to this Mr. Russell (National Geographic Maga- 

 zine, vol. iii, p. 92, Am. Geologist, March and May, 1892 ; 

 and this Journal, March, 1892) reports from the great Mala- 

 spina glacier, whose foot spreads out over an area of 1,500 

 square miles on the low lands southeast of Mt. St. Elias, that 

 on the belt of morainic accumulations which conceal the ex- 

 treme margin of the glacier for a width of five miles or more 

 there is a dense forest growth. This forest has every appear- 

 ance of considerable age. It consists principally of spruce 

 trees, some of which are three feet through, but there are 

 many alders " and a great variety of shrubs and bushes, to- 

 gether with rank ferns which grow so densely that one can 

 scarcely force a passage through them." (This Journal, p. 

 178.) In many places this vegetation is on a moraine which 

 is underlaid by ice not less than a thousand feet in thickness. 

 These forests appear also on the north border of the glacier. 

 The whole area of ice observed by Mr. Russell to be covered 

 by forests was estimated at from twenty to twenty-five miles. 

 Such facts as these should make us hesitate about attributing 

 every forest bed buried in glacial deposits to a distinct glacial 

 period. In the complicated movements which doubtless at- 

 tended the advance and retreat of so vast an ice sheet there is 

 room for the burial of a great many forest beds, and Professor 

 Chamberlin is doubtless correct in thinking that those discov- 

 ered in the Mississippi Y alley may belong to several different 

 horizons. In my " Ice Age " (pp. 484-488), I have quoted at 

 length from the late Mr. Lesquereux to show that two or three 

 hundred years is ample time to allow for the accumulations of 

 peat which have been found embodied in glacial deposits. 

 (See also Penn. Ann. Geol. Report for 1885, pp. 106 to 114.) 



