JULY 30, 1897.] 
bodies present upon which the crystals may 
form. 
It seems probable that in these facts we 
have an explanation of the influence which 
vegetation appears to have upon the de- 
posit of silicious material in the pools of the 
geyser basins. The mere presence of the 
algal filaments as foreign bodies encourages 
the deposition of silica, and it naturally 
follows that the greatest amount of silica is 
thrown down where the vegetation is 
thickest. This gives us the entire secret of 
the peculiarities of columns and mouldings. 
As has been before described, it is the habit 
of algze in quiet water to grow up in tufts. 
A tuft once established leads to the deposi- 
tion of more silica at that particular spot, 
and soon there will be formed a little mound 
or cone, capped and covered by a mass of 
filament. The algal filaments always tend 
to grow upward in quiet water, if for no 
other reason because of the numerous 
bubbles of oxygen thrown off, which, be- 
coming entangled in the threads, tend to 
buoy them up. As the algal cap on top of 
a cone grows upward, more silica is laid 
down at its base, and soa column of de- 
posit gradually rises. When the cap of 
vegetation reaches the surface of the water, 
there is, after the habit of such forms, an 
immediate radiation of the filaments in all 
directions. Consequently, when the final 
deposit of silica is left upon the top of the 
column, it extends on all sides as an over- 
hanging capital. As the shaft of the pillar 
is covered with the sheet of vegetation, we 
can readily understand why it should 
thicken and why there might be irregular 
protuberances or even smaller columns 
rising at different levels along the sides of 
the larger. Of course, the algal growth will 
not be uniform on all sides of the pillars, 
any spot that is especially vigorous leaving 
a record for itself through a larger amount 
of mineral deposit. 
Much more must be known about the ex- 
SCIENCE. 
157 
act conditions of growth in these thermal 
waters, before the many peculiarities of the 
mineral deposits are explained. Buta new 
interest is added to the hot springs of Yel- 
lowstone Park and their deposits when one 
thinks of the parts these simple organisms 
play in the construction. 
Children of steam and scalded rock, a story you have 
to tell, 
Writ in the glare of sunshine bright, 
Sculptured and etched in marble white, 
Illuminated in colors bold, 
Richer than ever parchment old, 
Children of steam and scalded rock, what is the story 
you have to tell? 
Our legends are old, of greater age than the moun- 
tains round about. 
We have kept our secrets epochs long, 
They are not to be read by the passing throng. 
It is nothing to us what men may say. 
If they wish our story the price they must pay 
In hard brain work, ere the tales are told. We chal- 
lenge mankind to draw them out. 
Children of steam and scalded rock, your challenge 
must rest for the present age. 
I have scarcely broken the outer crust 
That covers the greater truth, but I trust 
Some man will follow and therein find 
Knowledge, that to the Present shall bind 
The Past with cords wherein entwine 
Threads of the perfect truth, divine. 
Children of steam and scalded rock, some man to 
come will accept thy gage. 
Brapitey Moore Davis. 
UNIVERSITY OF CHICAGO. 
RAREFIED AND CONDENSED ATR. 
AFTER reading Paul Guessfeldt’s enthusi- 
astic description of ‘mountain-ecstasy,’ as 
he calls it, which the rarefied air of high al- 
titudes produces and which he describes as 
consisting of ‘an increased sense of joy 
caused by an increased muscular activity, 
and a wonderful buoyancy of the feelings 
which at moments rises to ecstasy,’ we are 
tempted to follow him to those heights in 
order to experience these feelings which 
can be so easily obtained with a little phys- 
ical exertion. 
