CHAPTER XII. 
THE GEOLOGICAL HISTORY. 
Early Paleozoic conditions. — Silurian strata. — The great unconformity at the head of the Grand Caflon 
and its significance. — The beginning of the Carboniferous. — Inferences as to the condition of the 
region in Carboniferous time and during the Mesozoic. — Uniformity of conditions over great 
areas. — Diversity of character in the beds considered in respect to vertical range. — Shallovr 
waters throughout the entire period of deposition. — The conditions in Cretaceous time. — Coal and 
carbonaceous shales. — Constant position of the surface of deposition. — Paradoxical nature of 
some of the problems presented. — Views concerning the mode of deposition in shallow waters of 
great area. — Relative distribution of land and water at the close of the Cretaceous. — Disturb- 
ances at the termination of the Mesozoic. — Unconformity of the Eocene and Cretaceous. — The 
advent of Eocene time. — Change of waters from brackish to fresh. — Great extent of the Eocene 
lakes and the causes of their creation. — The manner in which the lake of the Plateau Country 
was determined and its basin isolated. — Wide extension of the uplifting movement in the west. — 
Long persistence of the lakes. — Extent of Eocene deposits. — Origin of the plateau drainage 
system. — Stability of position in the principal drainage channels. — The great erosion during late 
Eocene time and during the Miocene.— Results accomplished at the close of the Miocene. — Gen- 
eral method of the process of denudation. — Origin of the present Grand CaHon at the close of 
the Miocene. — Changes of climate from moist to arid.— Condition of the district at the beginning 
of the Pliocene. — Base level of erosion at that epoch. — Subsequent upheaval. — The development 
of the faults. — Coincidence of the faults and basaltic eruptions with the periods of upheaval. — 
Amount of uplift at this epoch. — Effect of the arid climate upon the topography. — The more 
recent upheaval and further development of faults. — Second period of base level. — The evolution 
of the Grand Canon. — Rapid excavation of the inner gorge. — The glacial period. — Its effects upon 
the drainage channels. 
We may now attempt the somewhat difficult task of extracting from 
the foregoing facts the history of the Grand Canon district. Primarily, my 
intention has been to reconstruct only its Tertiary history. But, as in 
human affairs the events of any limited period are linked with those which 
preceded them, so here the Tertiary history is rendered more intelligible by 
reviewing whatever knowledge we may possess of the events which pre- 
pared the way for it. Prior to Tertiary time the records are very obscure, 
and the conclusions we may draw concerning such remote events are very 
few and of the most general nature, yet not without value. 
Of the earlier Paleozoic conditions prevailing in the Plateau Province 
we know as yet but little. Already many perplexing problems have arisen 
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