FORESTRY. 



22? 



asthmatic people, and retains a temperature 

 of about 45 degrees the year around. The 

 pure air is caused by the wind at the en- 

 trance changing according to the rising and 

 falling of the barometer. There are places 

 where the current of air is always in and 

 others where it is always out. During a 

 storm the air current is down, and in fair 

 weather it is out, often so strong that it 

 will nearly blow one away from the en- 

 trance. At the same time, ioo feet from 

 the entrance the current will not blow out 

 ■a candle. 



At nearly every turn or angle there are 

 crevices leading away which can be opened 

 at small expense ; and from all appear- 

 ances exploration and opening of these 

 crevices can be carried on in a moderate 

 way for the next 10 years. None the less 

 1» cturesque and grand is Crystal cave, 

 which, like Wind cave in many respects, 

 is found in the Elk Creek canyon of the 

 Black hills, about 12 miles South of Dead- 

 wood. This cave is nearly as large as 

 \vind cave, and it is believed by some that 

 both are connected by subterranean pas- 

 sage ways. About 300 chambers have been 

 opened in this cave and in the neighbor- 

 hood of 50 passageways. The Black hills 

 afford a remarkable field for geological 

 research. In no other mountainous coun- 

 try can such a comprehensive idea be ob- 

 tained of structural formations of the 

 earth's surface. Deep canyons have been 

 cut through one formation after another, 

 thus revealing to the student the true geo- 

 logical conditions. 



FOREST ADVANCE. 



An interesting group of facts, involving 

 problems of great import, is embraced in 

 the rate at which forests in Alaska and 

 British Columbia have been and are yet 

 following up glacial retreat. The rate of 

 retreat of the one and of the advance of 

 the other are recorded in 2 ways : By the 

 growth and advance of trees ; and by the 

 increasing depth of forest litter and humus, 

 due to the 2, 3 or more generations of trees 

 which have grown since the morainic de- 

 bris, or glaciated surface, was left bare 

 by retreating ice. 



Following observations on mountains on 

 which the glaciers were small remnants, I 

 visited Alaska for the purpose of studying 

 these phenomena where they are best 

 marked in the Northern hemisphere. After 

 careful consideration of those glaciers 

 which would give _the most reliable types 

 and at the same time would be accessible 

 in the short period available, Mendenhall 

 glacier and its former bed were selected 

 for special study. The features herein de- 

 scribed for this locality are in general true 

 for immense areas which were observed 

 but not closely studied. Jt is true that jn 



some instances glacial advance has been 

 recorded by the destruction of young and 

 even full grown forests; but these instances 

 evidently mark fluctuations in the general 

 glacial retreat which is in progress. After 

 a slight advance the retreat is again taken 

 up, and for a limited period with greater 

 rapidity than marks the retreat of neigh- 

 boring glaciers. 



Mendenhall glacier, in latitude 58° 25' N., 

 longitude 134 30' W., occupies the upper 

 portion of a lateral channel putting off 

 Northeasterly from the North end of Gasti- 

 neau channel. The glacier once occupied 

 the whole of this lateral channel, but has re- 

 treated until its face is now some 4 miles 

 from the junction of the 2 channels. This 

 lower end is now entirely filled with glacial 

 debris and overgrown with alder, cotton- 

 wood, spruce, shrubs, marsh growth, etc. 

 The lower portion of the filled area is just 

 above tide level ; the upper is about 150 

 feet above tide level. 



The front of the glacier is some 3 miles 

 in length and of irregular, varying height. 

 Where long continued melting has taken 

 place the wall of ice is only 20 or 30 feet 

 high, and where masses of ice have recently 

 broken off it is several times these heights. 



During the 9 years preceding 1901 the re- 

 treat, as marked by a mining stake, has 

 been at the rate of 40 to 50 feet a year. 

 This rate of retreat is recorded for a far 

 greater period by the forest and scrub 

 growth which flourishes on the former bed 

 of the glacier, and on its enclosing slopes. 

 At a distance of about 3 miles from the 

 present face of the glacier quite a forest of 

 spruce trees has grown, many of which 

 have been cut for the mines on Douglas is- 

 land. Those now standing within 2 miles 

 of the face of the glacier are nearly full 

 grown and are evidently the only genera- 

 tion which has ever occupied the locality, 

 as there are no aged or fallen trunks, and 

 the forest litter and humus are thin and 

 coarse. The size of one of these trees and 

 its growth are as follows : 



At 25 years 9 inches in diameter. 

 " 50 " 16 



" 75 " 20.5 " 

 " 100 " 23 



" 125 " 25.5 " 



" 150 " 27.5 " 



" 175 " 30.5 " * " 

 " 209 " 32.3 " 



Other trees, not felled, were as much as 8 

 or 10 inches larger in diameter, but the one 

 measured was about an average. 



Advancing from 24 to one mile toward 

 the glacier, few trees could be found over 

 20 inches in diameter, or about 70 to 80 

 years old. Within the next l / 2 to % of a 

 mile the trees had decreased in age to sap- 

 lings 6 to 8 inches in diameter or about % 



