166 The American Geoloaist. Septembor, 1S97 
Not less interesting tiian the forms of the dej)osits. and far 
more beautiful are the colors which are in large part due to 
the algffi. We are not surprised that grass is green, or that 
when the chill of winter strikes the leaves of the forest they 
turn to yellows and reds and golden hues. No more wonder- 
ful is it, though perchance more surprising, that plants which 
live in boiling water or warm water or cold water should have 
many colors. 
The Mammoth Hot Springs show against dazzling white 
deposits, patches of delicate pink or salmon hues which 
deepen along the edge of the basins, where moistened into 3'el- 
low, brown and red. The pools of the geyser region show red, 
rose, cream, brown, emerald, green and blue luies. 
The paint pots are reddish brown, umber, pink, blue and 
grey. 
The largest and most impressive mass however is seen in 
the Grand Canon. Here it is chiefly caused by mineral mat- 
ter. 
The great mass of rhyolite through which the waters of 
the Yellowstone have carved their way had been thoroughly 
decomposed by hot waters and gases. Thousands of steam- 
ing vents, solfataras, and furaaroles can be seen by one who 
has the daring to descend into the canon. Boiling water, 
scalding vapors and fiery gases had worked through and 
through, corroding, eating, destroying, decomposing and trans- 
forming the great mass. It was a rough experience. Then 
the weakened rock was attacked by the river and carved, 
worn and scoured. 
The rapidity with which it was worn away was due to the 
weak condition of the rock as well as to the great volume of 
rapidly running water and the rapidity has resulted in steep 
sides, sharp pinnacles and freshness of coloring. The spires 
and minarets have not had time to be leveled and the steep- 
ness of sides prevents their being overrun with vegetation or 
covered with faded materials. 
The result is the scene which charms the beholder. 
The grand canon of the Arkansas is impressive. The 
solemn grandeur of the Yosemite overwhelms and fills the 
mind with thoughts of vastness and sublimity. But the beau- 
ty of the Yellowstone charms and delights and thrills. As by 
