This ice-cliff or barrier was followed by Captain Ross as far as 198° west longitude, and found to preserve very much the same character during the whole of that distance. On the lithographic view of this great ice-sheet given in Ross's work it is described as "part of the South Polar Barrier, one hundred and eighty feet above the sea-level, one thousand feet thick, and four hundred and fifty miles in length." A similar vertical wall of ice was seen by D'Urville, off the coast of Adelie Land. He thus describes it: "Its appearance was astonishing. We perceived a cliff having a uniform elevation of from one hundred to one hundred and fifty feet, forming a long line extending off to the west.... Thus for more than twelve hours we had followed this wall of ice, and found its sides everywhere perfectly vertical and its summit horizontal. Not the smallest irregularity, not the most inconsiderable elevation, broke its uniformity for the twenty leagues of distance which we followed it during the day, although we passed it occasionally at a distance of only two or three miles, so that we could make out with ease its smallest irregularities. Some large pieces of ice were lying along the side of this frozen coast; but, on the whole, there was open sea in the offing." [AH] [Footnote AH: Whitney's Climatic Changes, pp. 315, 316.] [Illustration: Fig. 10.--Iceberg in the Antarctic Ocean.] _North America._--In North America living glaciers begin to appear in the Sierra Nevada Mountains, in the vicinity of the Yosemite Park, in central California. Here the conditions necessary for the production of glaciers are favourable, namely, a high altitude, snow-fields of considerable extent, and unobstructed exposure to the moisture-laden currents of air from the Pacific Ocean. Sixteen glaciers of small size have been noted among the summits to the east of the Yosemite; but none of them descend much below the eleven-thousand-foot line, and none of them are over a mile in length. Indeed, they are so small, and their motion is so slight, that it is a question whether or not they are to be classed with true glaciers. Owing to the comparatively low elevation of the Sierra Nevada north of Tuolumne County, California, no other living glaciers are found until reaching Mount Shasta, in the extreme northern part of the State. This is a volcanic peak, rising fourteen thousand five hundred feet above the sea, and having no peaks within forty miles of it as high as ten thousand feet; yet so abundant is the snow-fall that as many as five glaciers are found upon its northern side, some of them being as much as three miles long and extending as low down as the eight-thousand-foot level. Upon the southern side glaciers are so completely absent that Professor Whitney ascended the mountain and remained in perfect ignorance of its glacial system. In 1870 Mr. Clarence King first discovered and described them on the northern side.