325 
nitrogen and a rise in nitrates and in the oxygen consumed,result 
ing from the introduction of storm waters and silt. The temper- 
atures remain at or near the winter minimum, rising slightly 
with access of storm water. The total movement in levels is 6 
ft., but the rise is so gradual that a considerable development of 
the winter plankton appears. This brings the monthly aver- 
age up to .45 cm.‘ per m.*, an amount over twice that record- 
ed in 1899 and forty-five-fold greater. than that in the flood 
of 1896. The occasion for the greater production in this 
year is, it seems, the greater enrichment of the waters (though 
not in nitrates), the lower levels, and the slighter current, the 
latter affording time for breeding even upon the slowly rising 
flood. The same or even less rate of rise at higher levels—e. g. 
1899—would be attended by a more rapid current with lessened 
time for production. 
The February pulse hasa duration of 35 days,—from Jan. 
25 to March 1,—with a maximum amplitude of .67 em. per m.* 
on the 3d. Its mean lies on the 7th, 16 days after that of the 
preceding pulse. This is a month of almost continual rise, 
there being only a slight cessation in the first week. The total 
movement in levels is 5.1 ft., of which the greater part is above 
bank height, and leads to extensive overflow. The large 
amounts of silt carried (Pl. XII.) testify to the extent of the 
overtiow and the access of flood waters of recent origin. These 
result in a continued reduction in free ammonia and chlorine, 
both of which reach approximately normal levels at the close 
of the month. Nitrates rise with access of flood waters, and 
the nitrites continue to decline, while the oxygen consumed 
and organic nitrogen rise with the increase of silt. Tempera- 
tures remain at the winter minimum throughout the month, 
and an imperfect and disintegrating ice-sheet covers the stream 
during a part of the month. The effect of the rising levels, 
access of recent flood waters, increased current and great vol- 
ume of silt is seen in the falling off of the plankton content 
to a minimum of .02 em’. per m.* on March 1. The incipient 
pulse of production of an amplitude exceptional for this season 
