LETTER TO THE SECRETAEY. XXIII 



ably extended over the entire district, bnt are now either concealed by 

 overlying volcanic rock or have been removed by erosion. A number 

 of specimens of fossil plants obtained in different portions of the park 

 in 1872, and identified by Professor Lesquereux, indicate the existence 

 of the Laramie or Fort Union group, i^umerous specimens of the genera 

 Fopidus, Ficus, BJianimis, Jtiglans, Salix, Sahal, &c., were found in shales 

 or slates partially changed by contact with eruptive rocks. The map 

 shows very clearly the character of the lake beds as well as the more 

 modern deposits, and the report of Mr. Holmes, with his graphic illus- 

 trations, renders them very instructive. Even here, at the very sources 

 of the largest rivers in the most elevated areas of the West, the water 

 area of the lakes has diminished nearly one-half, as the old outline shows. 

 The restoration of the ancient lakes in the dry region of the Great Basin, 

 by Mr. G. K. Gilbert, present remarkable examples of the difference in 

 size between the ancient condition and the jjresent. 



Dr. Peale's report on thermal springs gives a detailed description of 

 all the springs and geysers, of any importance, found in the Yellowstone 

 National Park. On the maps of the different geyser basins accompany- 

 ing his report, the springs are indicated by numbers which coi respond 

 with those given to them in the text, so that hereafter there ought to be 

 no difficulty in identifying the individual springs and geysers. 



The descriptions of the geysers include observations made since 1878, 

 up to and including those made in the year 1881. 



Dr. Peale spent about one month in actual work on the springs and 

 geysers, a considerable portion of this time being devoted to assisting 

 Mr. Mushbach, who did the topographical field work for the preparation 

 of the maps. The rest of the time was occupied in studying the various 

 spring areas. He describes and tabulates over 2,000 springs and 71 

 geysers. The most interesting of these are shown in the plates and 

 figures illustrating his report. It ought never to be necessary to repeat 

 this preliminary work in the Park. What remains to be done is to start 

 a series of close and detailed observations protracted through a number 

 of consecutive years, with a view to determine, if possible, the laws gov- 

 erning geyseric action. 



In the second part of his report he brings together, in a few brief 

 chapters, short descriptions of the thermal springs of the globe, tracing 

 their connection with volcanic action, dwelling more particularly on the 

 Iceland and JSTew Zealand regions. 



In his third part, under the title thermo-hydrology, he takes up the 

 general subject of thermal springs, the color of water, source of heat, 

 &c., and compares the Yellowstone National Park with other hot-spring 

 areas, especially those of Iceland and New Zealand. Chapters are in- 

 cluded giving the analyses of the waters and deposits from the s])rings 

 of the Park, and the last section is devoted to the special consideration 

 of geysers, giving the theories and treating of the peculiarities of their 

 eruptions and the influences modifying them. 



