642 THE ANCIENT LAKES OF WESTERN AMERICA: 
this history are however, in a great measure, yet to be sup- 
plied ; inasmuch as the great area of our western possessions 
is still but very partially explored, and it is certain that it 
forms a great treasure-house of geological knowledge, from 
which many generations will draw fresh and interesting 
material before its riches shall be exhausted. 
The enlightened measures adopted by our Government for 
the exploration of the public domain, the organization and 
thorough equipment of the numerous surveying parties that 
have traversed the region west of the Mississippi within the 
last twenty years, together with the more extensive explora- 
tions by private enterprise of our great mining districts, 
have resulted in giving us materials from which an outline 
sketch can now be made that may be accepted as in all its 
essential particulars, accurate and worthy of confidence. 
It has happened to me to be connected with three òf the 
Government surveys, to which I have referred, and to spend 
several years in traversing the great area lying between the 
Columbia River and the Gulf of Mexico. The observations 
which I have made on the geological structure of our West- 
ern Territories supplement, in a somewhat remarkable way, 
those made by Dr. Hayden, so that taken together, our re- 
ports embody the results of a reconnoissance stretching over 
nearly the whole of our vast possessions west of the Missis- 
sippi. 
Our knowledge of the geology of this region has also been 
largely increased by the no less important contributions of 
other explorers. Among those who deserve most honorable 
mention in this connection are Mr. George Gibbs, to whom 
we are indebted for most that we kdo: of the geology of 
Washington Territory; to Professors W. P. Blake and 
Thomas. Antisell, to Prof. Whitney and the other members 
of the California Geological Survey; to Baron Richtofen, 
the lamented Rémond, Drs. Shiel, Wislizenus, and others. 
The results obtained by the last, largest and best organ- 
ized party which has been engaged in Western explorations, 
