132 GROVE KARL GILBERT— DAVIS tM " M0IB8 [ v I i A "att 



events was made clear by a diagram and explanatory text, in which the whole story was epito- 

 mized: After a very long prelacustrine arid period, during which a great erosion of the sur- 

 rounding mountains was accomplished and large piedmont alluvial fans were formed, came the 

 first lacustrine epoch of relatively long duration and moderate humidity, causing a rise of the 

 lake to a high level but without overflow for its waters, which therefore remained saline; the 

 shore deposits of this epoch are not now decipherable, but the bottom deposits are represented 

 by 90 feet of yellow clay; then came an intermediate arid period causing the disappearance of 

 the lake, the deposition of its salts, and their burial under inwashed sediments; next, the second 

 lacustrine epoch, of shorter duration and more pronounced humidity, causing the gradual rise 

 of the lake and the formation of an ascending series of superposed shore terraces until the 

 Bonneville level was reached, 90 feet above the highest record of the first humid epoch ; there- 

 upon overflow took place at Red Rock Pass, and the outlet channel was rapidly cut down in 

 the weak material first met, but when the lake had been lowered 365 feet a body of resistant 

 limestone was encountered in the channel bed and further lowering was practically arrested; 

 the lake then long remained at the level where the strong Provo beaches were formed, until the 

 desiccating climate of the present postlacustrine epoch set in and the great sheet of water was 

 reduced to about its present small dimensions. Thus the results of long-continued field studies 

 and of much reflection upon them were simply and compactly summarized. 



In the illustrations of this report the abandoned shore lines of Lake Bonneville were for 

 the first time revealed to distant readers in all their marvelous magnitude and distinctness. 

 One plate, however — a woodcut which appears to have been misinterpreted by the engraver — 

 is curiously erroneous in representing a large pre-Bonneville alluvial fan with its apex built 

 up against the mountain slope a little to one side of the valley from which its detritus is de- 

 rived, leaving the other side of the valley too far removed and exposed to too low a level. A 

 late chapter treats the relation of lake history to mountain building and presents a most edi- 

 fying discussion of catastrophic and uniformitarian views; it was here the belief was expresssed 

 that " the Wasatch range, the greatest mountain mass of Utah, has recently increased in height 

 and presumably is still growing." Reference to this chapter will be made again in a later dis- 

 cussion of the basin ranges. 



THE TOPOGRAPHIC FEATURES OF LAKE SHORES 



A chapter from the final Monograph of Lake Bonneville on " The topographic features of 

 lake shores" was printed in advance in the fifth annual report of the survey (1884), and gave 

 delight as well as information to many readers; it furthermore made clear Gilbert's predomi- 

 nant interest in physiography as contrasted to historical geology, and it developed in abundant 

 detail the thesis earlier stated in the Powell-like phrase: "There is a topography of the land 

 and a topography of the water." All manner of lake-shore forms were described and explained 

 with a fullness and a clearness that were both satisfying and gratifying, and that contributed 

 greatly to confirm the awakening conception of land sculpture as a worth-while study to which 

 geographers as well as geologists must give heed. The treatment throughout was thoroughly 

 Gilbertian in its breadth and deliberation, especially in the pages devoted to the discrimination 

 of lake-shore features from imitative features of other origins. 



Two peculiar features, the V terrace and the V bar, for which, the text states, "no satis- 

 factory explanation has been reached," were really better understood than that phrase would 

 imply; for although the cause of the eddying currents to which they may with much confi- 

 dence be ascribed was not discovered, the responsibility of such currents for the V-like forms 

 appears to have been clearly understood, witness the statement: 



The formative currents must have diverged from the shore at one or both the landward angles of the terrace, 

 but the condition determining this divergence does not appear. 



Yet although a reasonable origin was thus found for these peculiar forms as well as for 

 all others by which normal lake shores — that is, shores of lakes that have not been excavated 

 by glacial action — are characterized, they are all treated as ready-made products; the earlier 



