. The continent we live on. Physical geography; Natural history. hering in flight. The group courtship displays of these birds are among the most spectacular in the animal kingdom. During breeding season, the colorful air sacs at the sides of the necks are (as shown above and below) inflated with air to a remarkable size. Its trial introduction into other areas has not been successful. indicates ihjt the climate there was at no time wet. Indeed was fairly arid at least till the comparatively brief pluvial periods of the Pleistocene. To have cut the canyon, therefore, either the whole area must
. The continent we live on. Physical geography; Natural history. hering in flight. The group courtship displays of these birds are among the most spectacular in the animal kingdom. During breeding season, the colorful air sacs at the sides of the necks are (as shown above and below) inflated with air to a remarkable size. Its trial introduction into other areas has not been successful. indicates ihjt the climate there was at no time wet. Indeed was fairly arid at least till the comparatively brief pluvial periods of the Pleistocene. To have cut the canyon, therefore, either the whole area must have been at a vastly greater elevation to give the river sufficient power, or it must have taken much longer to form. Neither the melting of the montane glaciers nor the pluvial periods of the Pleistocene could have provided enough water to do the job without getting ponded, and if they were thus con- tained temporarily, they would have cut a straight rather than a meandering channel through the mountains when they burst out. The drainage pattern left on the plateau certainly seems to indicate ponding and sudden drainage, for it exactly resembles that left on the floor of any pond that has suddenly been emptied by the bursting of a dam. Yet none of these suggestions really explains this vast natural phenomenon, and especially how it managed to form into a serpentine gutter and still cut through the hardest of rocks for scores of miles to a considerable depth at its base level. It gives one an almost eerie sensation to ponder such almost planetary concepts as one stands on the rim of this great canyon at sundown and strains one's eyes through the pink and mauve miasma that here so confuses the last slanting rays of the sun. There is a great and vast calm and stillness that usually fills the canyon to its brim. Above may be blue sky, wheeling swallows and eagles, and all around on the plateau are stately pine forests, alive with raucous pifion jays, industrious sapsuckers, and
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