126 GROVE KARL GILBERT— DAVIS tME1!OIES [v N o A L T xxt 



Hence, if the lake episode were both recent and brief, a long nonlacustrine period must 

 have gone before it. In the Wheeler report, the prelacustrine, lacustrine, and postlacustrine 

 intervals are given as roughly proportional to 50, 10, and 1. It was evidently during the pre- 

 lacustrine period that the great amount of intermont aggradation, mentioned above in the 

 account of the basin ranges, must have taken place. 



Singularly enough, the warping of the Bonneville shore lines appears to have been detected 

 in the summer of 1872 about a month earlier than the date of the above notes, when the wave- 

 cut benches on the Oquirrh Range, 15 or 20 miles to the west, were in sight from the corre- 

 sponding benches on the flanks of the Wasatch Range near Salt Lake City. A first record is 

 here corrected by a second. The first reads: 



My impression is that the upper beach is continuous & level and only depressed in the distance by the 

 curvature [of the earth]. 



But later in the same day, after levels had been sighted across the depression between the 

 two ranges and earth curvature and refraction had been allowed for, it was noted : 



From this it appears that the beach near Camp Douglass [not far from Salt Lake City] is 76.5 ft higher 

 than on the Oquirrh Range. The distance may have been a little underestimated & the refraction overesti- 

 mated. The allowance for refraction — V7 of that for curvature — may apply only at sea level. 



Later measurements reduced the difference of altitude to a smaller measure, and closer 

 study of the ground discovered a 50-foot post-Bonneville fault along the base of the Wasatch 

 which had to be allowed for; but a difference of 22 feet still remained to be explained by warp- 

 ing. A problem of crustal warping was thus opened, to which Gilbert later devoted much 

 thought and from which he turned aside with regret when other duties held him in the East. 



A special phase of this same problem is alluded to in the Wheeler report, in which the name, 

 Bonneville, was first proposed for the extinct lake. After an account of the desert plain on which 

 the shallow water sheet of the present Great Salt Lake lies, attention was called to the position 

 of the lake on the eastern part of the plain as giving " evidence of the novelty of the present 

 relation of altitudes of different portions of the plain, which is far from an equilibrium. Nearly 

 the whole present increment [of detritus] to the desert floor comes from beyond [east of] the 

 Wasatch Mountains, and is deposited ... on the eastern margin of the lake. Since the lake 

 has no outlet, but parts with its surplus by evaporation, its area rather than its level tends to 

 constancy" — a very neat point, that — "and as the eastern shore increases, the water will rise, 

 pari 2)assu, and encroach on the western " (66). The eccentric position of the present lake was 

 evidently taken to indicate a recent warping of the area near the mountains, whereby the aggra- 

 dation of that part of the basin floor had been in part counteracted. Reference was made on a 

 later page to the probable deformation of the Bonneville beach, which was thought to be 300 

 feet higher in a southern arm than farther northeast; and it was noted that if future observation 

 confirms these inferences, the deformed beaches "will have special interest as the record, in the 

 middle of the continent, of undulations of the solid earth, produced at so late a geological date 

 that we may presume them identical with changes now transpiring" (93). This topic was fully 

 discussed in the final statement of the Bonneville problem and was made the subject of an 

 important address on scientific method in 1885, as will be told below. 



THE BONNEVILLE OUTLET 



An overflow for certain stages of Lake Bonneville was early inferred because of the long 

 maintenance of its surface at certain levels, as indicated by the strongest shore fines (Wheeler, 

 III, 90) ; and a northward outlet was suspected by various observers from what was known of 

 the general "lay of the land." This aspect of the problem had evidently been talked over with 

 Powell; for at the opening of the second season of field work on the Powell survey, Gilbert 

 appears to have been authorized to make a northward detour from Salt Lake City in search of 

 the suspected point of Bonneville overflow, before crossing the mountains and plateaus to the 

 east of the city on the way to the Henry Mountains, which were his main object of study that 

 year. The outlet was thus in August, 1876, proved to be, as Bradley of the Hayden survey had 



