1884.] NATURAL SCIENCES OF PHILADELPHIA. Y9 



covered b}' an ice-sheet for a quarter of a century or more, and 

 the plants beneath retain full vital powers. 



By referring again to my remarks on some geological features 

 of this part of Alaska (page 183, Proc. Ac, as cited), it will be seen 

 by a sunken forest of apparently modern trees there is reason to 

 believe that in comparatively recent times this peninsula was 

 clothed with a rich vegetation — that it was of a sudden partially 

 submerged and perhaps as suddenly elevated again a little — and 

 that all these changes have been the work of but a few hundred 

 years. The plants in question have probably survived through 

 all these changes, though perhaps wholly ice-covered at times, 

 and have not been brought here by modern agencies ; and if these 

 suggestions, which are offered only as great probabilities, should 

 get fuller confirmation from any one in the future who may have 

 opportunities of going more fully into an investigation of the 

 spot, it will give additional interest to the study of botany in 

 connection with the great changes which have been going on over 

 the surface of our globe. 



From other botanical evidences which southeastern Alaska 

 afl[brds, I am inclined to believe that geological changes in this 

 section have not required the long periods to effect which geolo- 

 gists usually demand. In the vicinity of the Davidson Glacier, 

 a little below Pyramid Harbor, layers of ice maybe seen covered 

 by sand and earth, and prevented from rapid thawing — only an 

 occasional spot showing the icy bed beneath — and yet alder and 

 other plants grow within a few hundred yards. On the other 

 hand, near the Muir Glacier, at the point where the river-bed 

 beneath the ice diverges from the glacier's direct course, the 

 only sign of arborescent vegetation is from a few score of willow- 

 bushes, scattered on the mountain-side. Beneath the drift, hun- 

 dreds of feet below, is a forest buried as it grew. Pines, alders, 

 and similar plants spread so readily in this region, that these 

 bare hill-sides would assuredly be clothed thickly with a forest 

 vegetation, thus replacing the forests which have been swept away, 

 if there had been time enough for the purpose. The immense 

 area and great depth of these treeless drift formations would 

 surely be regarded as requiring perhaps many centuries for 

 deposit, but for the evidence which the botanical observations 

 afford that the whole change must have taken place within very 

 I'ecent times. 



