REPORT OF THE SECRETARY. 73 



action, that the practical knowledge thus obtained might be used in the 

 study of the extinct volcanoes of our western coast. His assistant, Mr. 

 Diller, took the field at Red Bluff, Cal., early in July, and immediately 

 began the study of Lassen's Butte. The plain around Bed Bluff' is vol- 

 canic conglomerate of andesitic fragments, which formation extends for 

 25 miles eastward. During the latter part of the month he was en- 

 gaged in the examination of the region surrounding Mount Shasta. 

 Later, he made a geologic reconnaissance of the Cascade range. Inter- 

 esting studies were made of the faults on the eastward side of the range, 

 near Klamath Lake. In September he visited Union Peak, Mount 

 Thielson, Crescent and Summit Lakes, and Diamond Peak. Mount 

 Thielson proved to be a very interesting ruined crater of large propor- 

 tions. From Diamond Peak he proceeded to the group of volcanic 

 cones known as the " Three Sisters." Here both Mr. Diller and his 

 assistant, Mr. Hayden, met with an accident which obliged them to 

 suspend work. Later in the season the reconnaissance was resumed 

 and the west side of the range examined from Portland, Oregon, to Bed 

 Bluff, California. 



District of the Great Basin. — The work in this division has consisted 

 for several years in the investigation of the system of lakes which in 

 Quaternary time occupied so many of the valleys. This work is now 

 so far advanced that it is believed the most important generalizations 

 have been reached ; and the Director decided to close it as a means of 

 enabling him to increase the working force on the Atlantic coast. The 

 corps was therefore reduced early in the year, and those who remained 

 were instructed to devote the season to supplementing the material 

 already gathered so as to put it in the best shape for publication. The 

 office at Salt Lake City, which had been the base of operations for the 

 division, was closed in June. 



Mr. G. K. Gilbert, geologist iu charge, took the field soon after, visit- 

 ing in Northern Utah, Northern Nevada, and the Mono Basin of Cali- 

 fornia, localities necessary to complement his earlier notes. 



He was accompanied in Utah and Nevada by Mr. B. Ellsworth Call, 

 who is temporarily attached to the survey for the purpose of studying 

 the molluscan faunas of the Quaternary lakes. The Quaternary shells 

 are all of existing fresh-water species, but are depauperate as compared 

 with their modern representatives in the same region; and the problem 

 undertaken by Mr. Call is to determine the climatic conditions indicated 

 by this depauperization. 



Mr. Israel C. Russell has had immediate charge of the investigation 

 of Lake Lahontan, the Quaternary ancestor of Pyramid, Carson, and 

 Walker Lakes, and also of the investigation of the Quaternary history 

 of the Mono Lake Basin. He devoted the summer to the completion 

 of his field examinations. The six Quaternary glaciers which debouched 

 into Mono Valley were studied in detail and traced to their common 



