JuLy 30, 1897.] 
of the sun, there is still left the form of 
the growth in raised relief upon the traver- 
tine. 
In the shallow pools, only a few inches 
deep, one may find the most delicate frost- 
work creeping in from the side. Here the 
algal network is a skeleton upon which is 
laid a coating of calcium carbonate in the 
form of delicate granules. The filaments 
frequently have abeaded appearance, some- 
what similar to cobwebs covered with mi- 
nute drops of dew. ‘The effects are par- 
ticularly striking when a stream of water 
suddenly spreads out over a flat surface. 
Then the frosted growths radiate out from 
acommon point and the effectis sufficiently 
prominent to give rise to the term ‘fan’ 
that is applied to such figures. Of course, 
the more delicate patterns upon the forma- 
tion are not lasting. The wear and tear of 
the summer tourist season, and the freeze- 
up in the winter, break the lace work, but 
it is quickly renewed every spring. Indeed, 
there is opportunity for the exhibition of 
taste in the judicious distribution of the 
hot streams over the older portions of the 
formation. They could readily be kept in 
repair, for fresh deposits are laid down 
with astonishing rapidity. 
We now pass to the consideration of the 
silicious formations of the geyser basin and 
here we encounter some peculiar problems. 
The water comes forth boiling hot and 
supersaturated with silicious matter. There 
is no question but what some of this must 
be thrown down from the solution as the 
water cools. Indeed, one may sometimes 
find soft deposits of a gelatinous nature 
around the vents of various springs and 
geysers, apparently thrown out by a sudden 
discharge. Evaporation alone would make 
possible the gradual building-up of the in- 
interesting cones around the orifices of 
geysers. However, the deposition as a rule 
must go on very slowly, and the calculation 
has been made that in certain instances not 
SCIENCE. 
155 
more than one-sixteenth of an inch is de- 
posited each year. 
But our problems are concerned with the 
beautiful transparent pools scattered over 
the formation. Their water is as clear as 
crystal and the mineral matter on the slop- 
ing sides is as firm and hard as chalcedony. 
There is no vegetation in the hottest of 
these pools, but where the water has cooled 
down a few degrees one may find abundant 
growths of alge. There are membranous 
patches of various shades of green and 
masses of yellowish jelly. and also tufts of 
very delicate filaments that hold many 
bubbles of gas entangled in their meshes, 
making them rise up like small balloons 
held down by numerous cords. There are 
many peculiarities about these pools that 
make them very interesting. The sides 
are frequently moulded into curious figures, 
giving reasons for such names as ‘ The Oak- 
leaf Spring,’ ‘The Aquarium,’ etc. 
But the most peculiar structures are pil- 
lars that stand up from the bottom of the 
basin. They are of various sizes, some 
merely slight cones that roughen the stony 
floor of the pools, others finger-like projec- 
tions. In its fully developed state the col- 
umn rises to the surface of the water. As 
it grows older it becomes gradually thicker 
until the mass of deposit resembles a small 
island in a miniature sea of hot water. 
Fig. 7 shows one of these shallow pools 
from which the water had been drained. 
There are many columns, large and small, 
present in this instance, and the figure 
illustrates a characteristic peculiarity, 
namely: that often the top of a pillar 
spreads out at the surface of the water in a 
form that resembles the umbrella-like top 
of a toadstool. 
How are these columns and the figures in 
raised relief formed? Have they any con- 
nection with the algal vegetation? Indi- 
rectly there is a very important relation. 
It is not probable that these algze secrete 
