In examining certain deposits containing alluvial gold which lie on the upper waters of the Missouri, in the state of Montana, my attention has been called to the occurrence of accumulations of loess now in process of formation. So far as their extent or depth is concerned, these layers of wind-blown material are hardly worthy of remark; but they have a peculiar value as indices of certain alterations of climate which have occurred in relatively recent times, and they are, moreover, agents of change in the regimen of the streams of that district. The facts which are here presented were gathered mainly in the district bordering on the Ruby river, commonly designated on the maps as the Stinking Water, a branch of the Jefferson, on the upper reaches of the Missouri, near Helena, and in the Butte district. Incidentally, notes were made in other parts of Montana . . .