TjiIc FiU'tnq In the Adii'Ohdaek Region. — Smyth. 89 
and decay of vegetation shonld not be overlooked. As soon as 
the water becomes sufBcientl}' shallow, water lillies spring up, 
and after these rushes and other water plants, all of which con- 
tribute something toward land making. As shoal water is replaced 
by land, the mosses develope in abundance and become an im- 
portant factor in raising the surface ; while at the .same time sedi- 
mentation becomes of less moment, being limited to periods of 
high water. Sometimes considerable portions of a vly are 
covered with this wet, spongy moss. The partially decayed moss, 
together with sediment deposited by floods, gradually raises the 
surface till it becomes sufficiently dry and firm to support 
grass and, finally, trees, of which tamarack is always most 
abundant. 
The conditions prevailing during the formation of a vly are 
sometimes favorable for the production of peat; and that it has 
formed has often been proved, as stated by Emmons.* In the 
particular region under consideration, it has never, to the writers 
knowledge, been sought for. As peat results from the accumu- 
lation of decomposing vegetable material, its formation would be 
confined chiefl}' to the later stages of vly building when sedi- 
mentation is of minor importance. 
A striking feature l)rought out 1)y the examination of these 
lakes is the great diflierence in the rate of filling inditt'erent cases. 
The time during which the process has been going on is the same 
for all, and yet the effect produced varies greatly. The expla- 
nation is self evident; the rate of filling depends upon several 
conditions, the most important being the number, size :ind cur- 
rent of inlets, and the character of the surface over which 
they flow. The etfect produced upon a lakes outline ])y a given 
amount of sediment depends upon the area and the depth of 
water. As there is the utmost variation in these conditions, 
there is a corresponding variation in the results attained in a 
given time. Thus, a lake which, like Wilmurt, receives most of 
its water ))y soakage through the soil, shows very little etfect of 
filling; while the lakes that are fed by swift streams alwa^'s show 
some surface change, even when deep and of considerable size. 
An apparent exception to this rule is shown in >Ietcalf lake, 
about two miles long, reached by a trail of a mile and a half from 
Big Rock. This lake is fed at its upper end by a considerable 
* Geol. of .\. v.. II. p. 417. 
