MARINE ALGA) OF BEAUFORT, N. C. 389 
range of variation. The averages, however, are probably fairly accurate, since they 
are obtained from a large number of readings where the errors probably balance each 
other. The general average, 1.0205, may, therefore, be taken as closely approximating 
the mean density of the water at the laboratory wharf. At other places in the harbor 
the density will, of course, be different from this. Since alge grow throughout the 
harbor, some of them will be exposed to greater densities and some to lesser densities 
than those recorded here. 
Several salinometer readings have been made by the author at other places in this 
region. While these have not the value of the daily records made at the laboratory 
wharf, they indicate the comparative density at other places. They are as follows: 
Newport River near “Green Rocky? low tide... ).04.. 10 MA 0 ohare ats I. o16 
North ‘River near Lenoxville low tide. .otisoesh. onine CUA ek I. 0188 
Pamlico Sdund,-Ocracoke low:tidess .vregigeinavc. oleleieciosscteas le madd. I. OIL 
Goralimeelolt Beautorts actpeh reppin cites tacit oi ean eumoias mys aeetaette corse icici I. 0242 
TURBIDITY. 
The water from the open ocean outside of the inlet contains a considerable amount 
of suspended matter, as is evident when this water is filtered, while the water within 
the harbor has still more fine, suspended matter and is, at times, very turbid. All 
rocks, shells, and posts under water are soon covered with a thick deposit, and at many 
places in the harbor the bottom is covered with mud upto a meter or more in depth. 
In the harbor and in Bogue Sound the amount of suspended matter seems to increase 
as we go farther from the inlet, while in the sound back of Shackleford Banks the water 
is decidedly clearer, owing to the strong current running in from the ocean at this place. 
Farther back in this sound the water is as turbid as in the harbor. 
This turbidity not only reduces the light penetrating the water but itself affects 
the vertical distribution of aige, since much of the suspended matter is deposited on 
all objects in the water. ‘The older portions of the broader alge (as Dictyota, Padina, 
the leaves of Sargassum) are more or less thickly covered by this mud settling from the 
water. 
MOVEMENTS OF WATER. 
The usual maximum range of tide (at the spring tides) is 0.97 m. (3.2 feet), the 
usual minimum range (at the neap tides) is 0.7 m. (2.3 feet), and the usual mean range 
is 0.82 m. (2.7 feet). The tides may, however, vary considerably from these figures, 
the actual height and range attained depending in part on the direction and strength 
of the wind. The greatest range observed by the author at the laboratory wharf is 
1.31 m. (4.3 feet). The smallest range observed is 0.48 m. (1.6 feet). Under excep- 
tional conditions the low tides are higher than the high tides recorded on other days 
in the same month, while at other times the tides are unusually low. Although there 
is not a very great difference in the height of water at high and low tides, there is a 
great difference in the amount of light reaching the alge at these times. Except on 
Shackleford jetties, where the water is clearer, no alge were found in the harbor below 
1.4 m. below low water, and the majority were found within 75 cm. below low water. 
Most of the alge have, therefore, about twice as much water over them at high tide 
as at low tide. Furthermore, during summer and autumn the greater number of alge 
grow almost up to the surface of the water at low tide. For these parts of the plants 
