The observations necessary to Dr. Wright's calculations were taken along the line of a railroad, which, very opportunely, had been constructed along the eastern cliff. Here for a distance of about two miles the course of the road runs diagonally down the face of the cliff, descending in that distance about two hundred feet, and in its descent laying bare the layers of shale upon which the observations must be made. Along the course of the road at this point, watchmen are continually employed to remove obstructions falling down or to give warning of danger when any large masses fall. The disintegration goes on much more rapidly in wet thawing weather than at other times of the year. Often in the spring the whole force of section hands is required for several days to dispose of the material of one single fall. At the rate of one-fourth of an inch a year of waste along this cliff there ought to fall slightly over six hundred cubic yards annually for each mile where the wall is 150 feet high. At this rate the enlargement at the terminal of the Gorge would take place, Dr. Wright estimates, in somewhat less than ten thousand years. No accounts have been kept by the railroad of the amount of fallen material, but some estimate can be made from the cost of removal of the falling stone, together with the observations of the watchmen, one of whom has been in the employ of the railroad in this capacity for twelve years, and also by noticing the distance to which the cliff has receded since the construction of the road.