academy op scences] n s GEOLOGICAL SUKVEY 131 



meaning as compared with that of an explanatory text, have contributed to give a greater 

 measure of certainty to the published interpretation of Bonneville history, as it is generally 

 understood among geological readers, than Gilbert himself, with his exceptional capacity for 

 balanced judgment, actually intended. 



PRELIMINARY REPORTS ON LAKE BONNEVILLE 



Progress in the discovery and the interpretation of the facts concerning Lake Bonneville 

 having now been outlined, an account may be given of the reports in which the history of the 

 lake was published. It should be here noted that field work had been substantially completed 

 in 1S80, for on November 16 of that year Gilbert wrote to King from Salt Lake City: 



The data for a final map of Lake Bonneville are now complete. Every part of the peripheral coast has 

 been seen by some member of the party, and all the principal islands have been determined. The altitude of 

 the highest water-line has been measured by spirit level at five new points and a good series of barometric obser- 

 vations has been made for its determination in the southernmost Escalante region. _ The difference of altitude 

 between Bonneville and Provo beaches has been measured by spirit level at twelve points. Local maps have 

 been made of seven different groups of wave-formed bars and at each of these a measured profile has been made 

 for the purpose of exhibiting the inter-relations of the strongest water-marks of the series. The comparative 

 study of these profiles is believed to have an important bearing on the question of the origin of certain of the 

 beaches. 



The time for office work and report writing had thus been reached. Yet so many and so 

 absorbing were the distractions by which Gilbert's attention was turned from the Bonneville 

 problem after his return to Washington in 1881 that 10 full years elapsed between the com- 

 pletion of field work and the appearance of the famous Bonneville monograph. 



The contents of the monograph were foreshadowed by several preliminary statements. 

 The earliest was in Gilbert's first administrative report to King, dated at Salt Lake City, Octo- 

 ber 1, 1880, and was so attractively phrased as to awake an expectant interest in the fuller 

 statement that was to follow. Two paragraphs from it may be quoted: 



The Great Salt Lake Desert and a congeries of valleys connected with it were filled with water at a period 

 so recent that the vestiges of the flood are little impaired at the present time. The sea cliffs that were covered 

 by the dash of the ancient waves are sea cliffs still, though they stand a thousand feet above the present level 

 of Great Salt Lake. The bars and beaches of sand and gravel that were built by the ancient currents are fur- 

 rowed here and there by the rains that have since fallen on them, but they are furrowed only, and not de- 

 stroyed; and the imagination is not strained to fill the gaps and restore their full contours. The fine silt that 

 settled quietly in the deeper waters still forms the floors of the valleys. To the geologist accustomed to speak 

 familiarly of millions of years, it is the veriest yesterday when all these things were wrought; nor can any one 

 who stands on the quartzite shingle of one of the old beaches, and contemplates the rounded pebbles, gleaming 

 with the self-same polish they received when the surf laid over them, fail to be impressed by the freshness of 

 the record. 



There is a topography of the land and a topography of the water. The forms of the land are sculptured 

 by the beating of the rain and by the flow of rills, and creeks, and rivers, and they have peculiar characters 

 accordant with their origin. The forms of the beds of lakes and oceans, and especially the forms of shores, are 

 sculptured by the sway of waves and currents, and are distinguished by characters equally peculiar. All the 

 hills and mountains above the shore line of Lake Bonneville bear witness of the play of subaerial agents, while 

 below that line the slopes betray their subaqueous shaping. There is a trenchant line between them, and their 

 peculiarities are beautifully contrasted. A careful inspection, however, shows that subaqueous characters are 

 superimposed on subaerial characters. The forms belonging to the dry land are continued down past the shore 

 line, and the sculpture of the lake has been superficially impressed on them without entirely obliterating them. 

 It is thus made evident that before the epoch of the lake, the land it covered was dry, just as it is now. The 

 lake had a beginning as well as an end. It came, it lingered long enough to make an unmistakable record, and 

 then it departed as it came. 



The expectations excited by the brief summary from which the preceding paragraphs are 

 quoted were well satisfied by the longer account published under the title, " Contributions to 

 the history of Lake Bonneville," in the first one 8 of the many handsome and instructive annual 

 reports by which Powell's administration of the survey was characterized. The treatment here 

 given to the problem is concise and direct rather than argumentative, and thus places its read- 

 ers promptly in possession of the essential elements of Bonneville history. The succession of 



' 2d Ann. Rep. U. S. Geol. Survey, 1881, 169-200. 



