G. K. Gilbert — Inculcation of Scientific Method. 291 



cliffs wrought by these waves remain in a high state of preser- 

 vation to testify to the position of the ancient water margin. 

 Through the greater part of its extent this shore-line forms a 

 conspicuous feature in the topography of the country, and is 

 readily traceable. It has been actually traced out, surveyed, 

 and mapped with much care, and our knowledge of the old 

 lake is in many other respects definite and full. 



Its width from a few miles east of Great Salt Lake to the 

 west side of the Great Salt Lake desert was 125 miles. From 

 the mountains on the north of the desert to those on the south 

 its expanse was about the same, but it did not terminate with 

 the southerly mountains. It extended through them in several 

 straits and formed beyond a second and much smaller body of 

 water. The main body was 1,000 feet deep, the minor body 

 about 500 feet. 



Manifestly, when this old shore-line was made, all parts of 

 it lay in the same horizontal plane, with no other curvature 

 than that which belongs to the figure of the earth ; that is, all 

 parts of it were level. If it is not now level — if some parts 

 are higher than others, it seems equally manifest that there 

 have been local elevations or subsidences of the land. It is to 

 such differences of level in the shore-line as it stands, and to 

 their interpretation, that I desire to call your attention. 



As far as the eye can judge, the shore is still level, and so 

 long as no measurements were made its horizontality remained 

 unquestioned. The two geologists who were probably the first 

 to measure its height recorded their results in language imply- 

 ing no suspicion that more than one determination was neces- 

 sary. 



It happened that in the year of my first exploration of the 

 Bonneville area I saw the shore-line not only in the Salt Lake 

 basin but in the more southerly basin, and that I passed from 

 one basin to the other by a route that did not reveal their 

 connection. In doubt whether two lakes were under observa- 

 tion or only one, I sought to answer the question by determin- 

 ing the height of the shore-line in each, my instrument for the 

 purpose being the barometer. The verdict of the barometer 

 was that the southerly shore-line was somewhat higher than the 

 northerly, but the computations necessary to deduce it were 

 not made until the mutual continuity of the two shore-lines 

 had been ascertained by direct observation. The barometric 

 measurement was therefore superseded as an answer to the 

 original question, but it answered another which had not been 

 asked, for it indicated that the ancient shore at one point had 

 come to stand higher than at another. The postulate of hori- 

 zontality was thus overtiirown. 



An hypothesis immediately took its place. It is one of the 



