The only remaining theory of value is the one advocated by Professor Powell: that the phenomena are to be ascribed to the modification of the surface of the earth by the agency of man. The rise of the lake and the increase of streams have been observed since the settlement of the country by the white man, and the sage brush on the old storm line shows that they had not been carried to the same extent at any previous period in the century. They have coincided in time with the extension of the operations of civilization; and the settlers attach this idea to the facts in detail as well as in general. They have frequently told me that wherever and whenever a settlement was established, there followed in a few years an increase of the water supply, and these statements have been supported by such enumerations of details that they seem worthy of consideration. If they are well founded, the secret of the change will surely be found among the modifications incident to the operations of the settler. Similar testimony was gathered by Prof. Cyrus Thomas in 1869 in regard to the increase of water supply at the western edge of the plains, and the following conclusion appears in his report to Dr. Hayden (page 237 of the reprint of Dr. Hayden’s reports for 1867, 1868, and 1869): All this, it seems to me, must lead to the conclusion that since the territory [Colorado] has begun to be settled, towns and cities built up, farms cultivated, mines opened, and roads made and travelled, there has been a gradual increase of moisture. Be the cause what it may, unless it is assumed that there is a cycle of years through which there is an increase, and that there will be a corresponding decrease, the fact must be admitted upon this accumulated testimony. I therefore give it as my firm conviction that this increase is of a permanent nature, and not periodical, and that it has commenced within eight years past, and that it is in some way connected with the settlement of the country, and that as the population increases the moisture will increase. Notwithstanding the confidence of Professor Thomas’s conclusions, he appears to have reached them by a leap, for he makes no attempt to analyze the influence of civilized man on nature to which he appeals. Before we accept his results, it will be necessary to inquire in what way the white man has modified the conditions by which the water supply is controlled. To facilitate this inquiry, an attempt will be made to give a new and more convenient form to our expression of the amount of change for which it is necessary to account in the basin of Great Salt Lake.