AlAT 8, 1908] 



SCIENCE 



753 



filled in at its northern end by a large alluvial 

 fan. Since the streams which feed the lake 

 have their source in the snow and ice fields 

 high up on the adjacent mountains, they are 

 loaded with a considerable supply of rock 

 waste, which, by reason of their swift descent 

 down the steep mountain slopes, they can 

 easily wash into the valley. But as soon as 

 the water reaches the much gentler g^rade of 

 the valley floor, a great deal of the material, 

 which is too heavy to be borne farther, is 

 dropped, the coarser near the foot of the cas- 

 cades, the lighter at some distance. In spring, 

 when the volume of the rivers is much in- 

 creased, coarse fragments are swept farther 

 down the valley than they are in the summer 

 season. Furthermore, after the stream has 

 raised its bed in one place, a freshet may 

 cause it to break through its low walls and 

 begin building in a new direction. Evidence 

 of this swinging of the stream is abundant on 

 the surface of the Emerald Lake fan, in the 

 numerous forsaken channels that radiate from 

 its feeding point, or origin. 



The construction of the fan is carried on by 

 iwo streams which unite near the head of the 

 lake. That the west branch is the more effi- 

 cient is proved by the fact that the east branch 

 flows through a narrow marshy tract bounded 

 on the east by the steep valley walls and on 

 the west by the edge of the fan of the west 

 branch. In other words, the latter has shoved 

 the east branch against the eastern valley 

 walls. Eurthermore, the east stream has, near 

 the base of its cascades, a small fan of its 

 own. 



There is no doubt, then, that the main fan 

 is growing. At what rate this development is 

 going on is not certain; but it must be rela- 

 tively rapid, for, although trees of twenty or 

 thirty years are found on many parts of the 

 deposit, especially in the older portions, these 

 are generally rather thinly scattered. Vegeta- 

 tion is scarce because there has been little or 

 no rock decay. 



Emerald Lake was described above as occu- 

 pying a depression near the head of a glacial 

 valley. We may add that the fan is in the 

 northern half of this depression; that is, the 



lake and the fan together are situated in a 

 single basin. This is very evident in the field, 

 where the continuity of the bounding walls of 

 both fan and lake is most conspicuous. 



The northern border of the lake is marshy 

 because the finer sediments of the fan are laid 

 down here. Farther back these are being cov- 

 ered by coarser sand and pebbles. Hence a 

 vertical section through the fan would be that 

 of a typical lake basin, for in vertical succes- 

 sion the strata run from fine below to coarse 

 above. 



There are five facts, therefore, which indi- 

 cate that the lake is being filled in by the fan. 

 They are as follows: (1) the surface of the 

 fan is dissected by channels of recent forma- 

 tion; (2) the weaker stream has been pushed 

 against the valley wall; (3) the deposits are 

 fresh, and the vegetation is consequently 

 sparse; (4) the lake and the fan are in the 

 same depression; and (5) the structural rela- 

 tion between the lake and the fan is that of a 

 filling lake basin. The first three statements 

 denote recent change, while the last two refer 

 to the close connection between the sites of 

 the water and of the sediments. To-day Emer- 

 ald Lake appears to be about half its original 

 size. How soon it will be crowded out of 

 existence it is impossible to determine; but 

 that it must eventually disappear, unless some 

 unforeseen event occurs, seems inevitable. 

 Fred. H. Laheb 



Haevaed Univeesity 



BOTANICAL NOTES 

 SEASIDE LABORATORY WORK 



The combination of recreation with study 

 is so difficult in many places that it often 

 seems an act of cruelty to urge tired teachers 

 to engage in study during summer vaca- 

 tions. We work too hard for eight or nine 

 months, so that rest of some kind is often 

 absolutely necessary in order to avoid brain 

 fag. No doubt it would be a wiser' plan in 

 schools and colleges for both students and 

 teachers to work at a more leisurely rate, and 

 to keep it up the whole year, as is done in 

 other occupations, but as schools are con- 

 ducted at the present time teachers and 



