290 GROVE KARL GILBERT— DAVIS [Memo,b ^™xxY: 



convexity of hilltops, a physiographic problem the solution of which had eluded him long before 

 in the land-sculpture chapter of the Henry Mountains report; and the third treated anomalies 

 of gravity in relation to isostasy. The first two illustrated his usual combination of refined 

 observation in the field with delicate mental interpretation; the third introduced a new and 

 ingeniously devised postulate for geodetic discussions and exhibited his unusual capacity in 

 the treatment of mathematical questions. 



As to the two large investigations in California, it should be remembered that both of 

 them were begun before and finished after his illness in 1909. One was the experimental and 

 mathematical study of the transportation of detritus by running water; he had assistance in the 

 experimental work, but appears to have made all the elaborate calculations himself. This study, 

 in spite of the great amount of time and labor bestowed upon it, appears to have been like the 

 much earlier study of a three-station method of measuring heights with the barometer, less fruit- 

 ful than he had hoped it might be. The other was his truly wonderful study of the distribution of 

 hydraulic-mining debris, from its source in the beds of auriferous gravels on the marginal uplands 

 of the Sierra Nevada, along its devastating course on the valley plain of California, to its final scat 

 in the bay-head marshes and deltas of San Francisco Bay, and even to its far-reaching indirect 

 effect in the displacement of the submarine bar outside of the Golden Gate. Excepting the 

 aid of an assistant for a few days in recording tidal movements in the bay, it is all Gilbert's 

 own accomplishment. 



It may be remarked that just as there is a very brief mention in the Henry Mountains 

 report of the low value of that region economically, so here also a faint economic tinge is given 

 in a brief consideration of the relative values of agriculture as developed on diked areas of 

 bay-head marshlands and of commerce as dependent on the depth of water over the bar outside 

 the Golden Gate; and similarly the edifying discussion of the earthquake of 1906 had a certain 

 economic bearing in connection with the possibility of predicting shocks before they come and 

 of decreasing destruction when they come; but these economic touches were in all cases very 

 subordinate to what may be called the purely intellectual phases of his work, and never more 

 so than in the admirable study of hj^draulic-mining debris. Its contents have already been 

 analyzed in an earlier chapter, and it was there characterized as a rival of the Bonneville mono- 

 graph. It must be here praised again, for it is a marvelous combination of patient and laborious 

 observation with critical quantitative interpretation. In spite of the serious illness in 1909, 

 Gilbert's mental powers as here reflected seem undiminished in keenness, although they were 

 of less continuous action than in his maturity 30 years earlier. Great must have been the 

 consolation that he found in their exercise at a time when his capacity in other directions was 

 waning. If any readers of the present memoir, young or old, have not yet read that California 

 masterpiece of his, let them do so without delay. Furthermore, if the older of them have felt 

 that advancing age will either prevent or excuse them from going on with their own labors, let 

 them learn the lesson that Gilbert's last published report teaches, and look forward to their 

 still older years as a time of continued opportunity. Let them remember also that Gilbert, 

 on completing that last published report, at once entered UDon another study and kept it in 

 hand up to within a month of his death. 



gilbert's presidential addresses 



The addresses that Gilbert delivered before the various societies that elected him to their 

 presidency may be here reviewed in a group by themselves, although some of them have been 

 reviewed on the foregoing pages. They ought to be brought together and published in a single 

 volume, so valuable are they as original contributions to science and so beautifully do they 

 illustrate the breadth of his competency and the wisdom of his methods. The first was the 

 "Inculcation of scientific method by example," delivered before the Society of American Natu- 

 ralists, at Boston, in December, 1S85; it has been analyzed in an earlier chapter as an example 

 of unusual capacity in penetrating and impartial analysis, as well as of a fair-minded spirit 

 of scientific inquiry. The same society, having elected Gilbert as president for a second year, 



