longest, deepest, and most difficult of passage in every direction of any canyon in the world. The depth begins with a couple of hundred feet at Lee’s Ferry (mouth of the Paria), the head of Marble Canyon, and steadily deepens to some 3500 feet near the Little Colorado, where the sudden uplift of the Kaibab lends about 2000 feet more to the already magnificent gorge. Along the end of the Kaibab the walls, for a long distance, reach their greatest height, about 6000 feet, but the other side is considerably lower than the north all the way through. At the mouth of the Kanab the altitude of the river-bed is 1800 feet above the sea, showing a fall in the interval of 890 feet. The greatest declivity is about 210 feet in 10 miles, in what is termed the Kaibab division, extending from a point 10 miles below the Little Colorado to a point 58 miles farther down. Here the smooth stretches of river are long, the rapids short and violent. Here, also, is the “granite,” making the walls sombre, as the colour is slaty to black. At the mouth of Diamond Creek the river is still 1300 feet higher than the sea, giving a fall of 500 feet from the Kanab. There is another descent of 460 feet to the Grand Wash, and then 149 to the mouth of the Virgen. Next to the Kaibab division of the Grand Canyon, the greatest declivity occurs in the Uinta region, in the Canyon of Lodore. The profile of the river in these two districts is approximately given on page 57. The average depth of the Grand Canyon is about 4000 feet. Its width at the top varies from 4½ to 12 miles. This is the extreme outer cliff-line. The inner gorge is much narrower, at the Toroweap being only about 3500 feet. The river varies in width from 500 or 600 feet to 75 or 100. In this canyon is water-power enough to run the machinery of the world, and there is as much more in the canyons above. Character of the Mountains and High Plateau Regions of the Basin of the Colorado. Character of the Mountains and High Plateau Regions of the Basin of the Colorado. Photograph by J.K. HILLERS. Profile of the Colorado through the Grand Canyon. Profile of the Colorado through the Grand Canyon. Horizontal Scale: One Inch = 40 miles—Vertical: One Inch = 2000 feet. The altitude of Grand Wash is given about 60 feet too high. Looking across the Grand Canyon (Inner Gorge) near the Foot of the Toroweap. Looking across the Grand Canyon (Inner Gorge) near the Foot of the Toroweap. Depth 3000 feet. Photograph by J.K. HILLERS, U.S. Geol. Survey.