27 
A discussion of this species, maintaining it to be distinct from 
£. Americanus. 
Field Notes from the Colorado Desert. C.R. Orcutt. (Garden & 
Forest, iii. 558, 559). 
Formation of Travertine and Silicious Sinter by the Vegetation of 
Flot Springs. Walter H. Weed. (U.S. Geol. Surv., Ninth 
Ann. Rep., 619-676, illustrated. Also reprinted). 
The author begins by calling attention to the fact that the in- 
fluence of plant life in building up certain formations is frequently 
ignored, for the reason that it is only by a careful study of such 
formations while in actual process of construction that an ade- 
quate idea of this influence can be gained. It is no doubt for this 
reason that the subject has been heretofore neglected, and the 
author has taken full advantage of a comparatively unexplored 
field of investigation. The facts upon which this article is based 
were gathered in the Yellowstone region, but a general review of 
the literature of thermal spring vegetation precedes the author’s 
own observations. This vegetation is entirely algal, and in the 
Yellowstone region, does not occur at a temperature above 185° 
Far. Although this vegetation has been frequently noted and 
studied to a greater or less extent, its importance in the forma- 
tion of hot spring deposits does not seem to have received the at- 
tention which it deserves. Not only do the plants become en- 
crusted with the mineral matter, but by their abstraction of car- 
bonic acid from the water they hasten the deposition of the car- 
bonate of lime and thus become an important factor in the forma- 
tion of travertine. In fact, proof is given that in certain places 
travertine would not form but for the presence of plant life. In 
only two instances was it found that vegetation was not either 
directly or indirectly concerned in its formation. Of the numer- 
ous forms of travertine none show the vegetable origin more 
clearly than the fibrous tufa forming fan-like masses. If a frag- 
ment of this is dissolved in hydrochloric acid it shows that each of 
the fibres is formed of a single encrusted alga filament. In the 
formation of silicious sinter, the algae seem to act mostly by form- 
ing dams or other obstructions of gelatinous material, over which 
the sinter is deposited. Thus pillars are formed in the interior of 
pools and rims around the margins. The exact manner in which 
