528 Noble — Geology of the Grand Canyon, Arizona. 



in the cutting of this mighty gorge has almost blinded us to 

 the realization of the immensity of the vastly greater record 

 revealed in its walls. But the story told by the two intersect- 

 ing unconformities in the bottom of the gorge, — two ancient 

 cycles of sedimentation, uplift, and erosion carried to a finish, 

 separated by hopelessly lost intervals of time, resulting twice 

 in the planing down of lofty mountain ranges to the very core, 

 written vaguely at first on a blurred and time-worn record, and 

 later in an increasingly clearer and bolder hand, — the slow 

 accumulation of the strata of the Canyon wall on 'the floor of 

 the Paleozoic sea, the subsequently erased record of the accu- 

 mulation of vast thicknesses of Mesozoic and Eocene strata, 

 separated in turn by great intervals of erosion, and even the 

 " great denudation " which has stripped these ]ater strata back 

 fifty miles to the terraces of Utah — represents a lapse of time 

 compared with which the cutting of the Grand Canyon is but 

 the passing of an afternoon ; for in the light of present knowl- 

 edge it is safe to say that the Grand Canyon was entirely cut 

 since the time when, according to the fossil record, the remains 

 of man first appear on earth. 



Bibliography. 



Barrell, J. a. Journal of Geology, vol. xiv, 1906. 

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b. The Production of Asbestos in 1908. Mineral 

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 Ransome, F. L. a. Pre-Cambrian Sediments and Faults in the 

 Grand Canyon of the Colorado. Science, vol. xxvii, No. 

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b. Geology of the Globe Copper District, Ariz. Prof. 



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Auburn, N. Y., January, 1910. 



