In the lowermost foot of the deposit no ripple marks can be seen. But there appear some marks of sedges and other vegetation, and these are inclined to the west, as if the plants had been bent by an east wind. Just above the height to which the imprints of the vegetation extend, ripple marks begin to appear, running on a northeast-southwest course. They were made by a southeast wind, for their northwest slopes are the steeper. A little above this height some peculiar small elevations appear on one of the bedding planes, and slightly raised ridges run for a short distance to the northeast from each elevation, vanishing in the same direction (Fig. 6). A southwesterly current was unmistakably obstructed by the little elevations, and left the small trails of dust in their lee. Six inches higher up the wind comes more from the south, and for the next foot the ripples continue to gradually turn still more in the same direction so as to at last record a due south wind. At this point it suddenly changed and set in squarely from the west, for the ripples are turned north and south, with the steeper slopes to the east. This direction seems to have prevailed as long as the dust kept on falling. It appears to me that these successive changes are best explained as attendant upon the passage of a cyclone, or of what our daily weather maps call a "low area." Going by from west to east, on the north, it would at first cause an east wind. This would then gradually be turned to the south and then to the west. One such rotation of the wind generally lasts a day or two. The shower must then have kept on at least for the same length of time, if not longer (Fig. 7). [Illustration: FIG. 7.--CHANGES IN THE WIND AS RECORDED BY THE RIPPLE MARKS.] There is reason to believe that this catastrophe occurred in summer. No crayfish would be out making tracks during the cold months, and the fossil vegetation could hardly have left such plain marks if it had been buried by the dust during the winter. The most conspicuous of these marks are some triangular and Y-shaped molds of the stems and leaves of sedges. Siliceous skeletons of _chara_ and filamentous algæ were also found upon a close examination in some of these molds.