1897] ALGAL STALACTITES OF VELLOWSTONE NATIONAL PARK 195 
midium, or the like, is placed in a drop of water spread out on a 
surface, as ona mounting card, the filaments move away from each 
other so that they come to occupy the entire drop. In this moving 
about they arrange themselves in somewhat radial lines. This 
behavior on the part of these plants is frequently made use of 
in the preparation of dried mounts. A bell jar is placed over 
the card on which is the drop of water containing the alge. 
This prevents evaporation for a few hours, which is as long as 
the filaments remain in action. Whendried in this way the plant 
shows to very good advantage its texture and color. 
The geyser in which the stalactites were found was situated 
ona knoll near the summit of a hill. Generally, the vent of a 
geyser occupies the center of the built-up cone. In this case 
the aperture was in the side of the cone, the center of which was 
entire and mound-shaped. This resulted in there being formed 
a cavity a foot or two in diameter and winding or irregular in 
Shape. Since the opening was near the base of the cone, and 
small in comparison with the size of the cavity, only a limited 
amount of light could reach the interior. The geyser spurted 
hot water almost continuously, but in small quantities, which 
may have reached a height of a foot or two, had it not been 
intercepted by the dome of the deposit. As it was, the water 
struck the ceiling of the dome and most of it trickled back into 
the pit. A small stream of hot water issued from the vent with 
jets of steam. 
The action of a geyser may undergo frequent change during 
its period of existence with regard either to the force exerted in 
projecting the water, or to the amount of water thrown off at an 
eruption, or to the length of the interval between eruptions. 
Consequently, it is reasonable to suppose that this particular 
geyser at some previous stage projected its stream of water to 
a less height than at present, that is, so that it did not come in 
contact with the dome. The steam, under such circumstances, 
would have condensed on the cold surface of the ceiling of the 
dome, forming drops of water which evidently would not have 
quickly evaporated, since they were kept in a moist atmosphere 
