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t is a fairly even process； and yet there is slightly more pressure brought to bear under the southern portion； so that the whole mass has a slight tilt to the north。 Professor Salisbury found certain beds of rock at seven thousand eight hundred feet above sea level at the base of the San Francisco Mountains near Flagstaff。 Forty…five miles north； at the Grand Canyon； these same beds are only six thousand four hundred feet above sea level； while at the Vermilion Cliffs； another forty…five miles to the north； they are but four thousand four hundred feet above the sea。
Yet in spite of this northward tilt； when the eye ranges over the country to the south and west； from the upper porch of El Tovar； a large area of depression can clearly be seen； showing that surface erosion has planed away much of the upper crust。
The Plateau Region。 Now we are ready to take a look at the borders of the plateau region。 On the north； it extends into Utah； where still higher plateaus bound it。 To the west； it extends by gigantic steps into the desert region。 The main step is along the Grand Wash； near the one hundred and fourteenth meridian。 To the south； there is one glorious step； known as the Mogollon Escarpment （locally the Red Rock Country）； some three thousand feet high； which extends for a number of miles east and west； and then breaks down。 This step and broken levels lead to the irregular lands of Central and Southern Arizona。 On the east； the plateau extends to the Echo Cliffs beyond Marble Canyon； and as far as the ridge of the Continental Divide； where the Santa Fe crosses the Zuni Mountains； east of Gallup； N。 M。
Present Conditions。 With this general view of the great plateau in our mind's eye； we are prepared to examine present conditions at any given spot in the Canyon。 Let us； therefore； take a seat at El Tovar； and try to read a few pages of the stone book of Creation as opened there。 Suppose all this vast region at about sea level； and the uplift just beginning。 The course of the Colorado River is already well defined。 As the uplift continues； the cherty limestone and possibly the cross…bedded sandstone are both cut through； as the plateau slowly emerges。 Whether the process of uplift is slow or rapid； as soon as a stratum emerges； it becomes subject to the influences of weathering； and the uppermost strata appearing first； they are weathered most。 Hence the recession of the uppermost cliffs is greater than that of the cliffs lower down。 The differences in hardness and resistance to weathering are alone responsible for the step…like profile of cliffs and terraces。 The lower platform owes its width entirely to the rapid weathering and recession of the soft shales； which overlie the Tonto sandstones。 The red…wall limestone； on the other hand； remains standing out as a cliff because of its exceeding durability。
The Faults。 During the final uplift； the river cut through the Cambrian and Algonkian strata； and into the Granite Gorge as we find it to…day； and the process is still slowly going on。 During these various periods of uplift； there were other changes occurring。 Sometimes the uplift was uneven； certain parts of the plateau being lifted more rapidly than other parts； then occurred breaks in the strata； called faults。 There are a great number of these faults in the plateau country； most of them crossing the Canyon from north to south。 This faulting； as is readily seen； would produce cracks； and as the uneven uplift continued； the strata on one side of the crack would be lifted higher than the strata on the other side。 Or； the strata on one side of the crack would be uplifted； while the other would subside。
Bright Angel Fault。 El Tovar rests directly upon the strata affected by the Bright Angel Fault line。 On going down the Bright Angel Trail； one cannot fail to see； as he passes the tap of the cross…bedded sandstone； the break in the strata。 To the left it is fully one hundred and fifty to two hundred feet higher than it is on the right。 The same depression may be observed in driving out to Hopi； Point； or returning。 The stratum on which the road is made should be at the same level as the stratum on which El Tovar rests。
Fault at Bass Camp。 This fault is but one of a score or more on the plateau。 At Bass Camp there was a fault which displaced the strata on each side of the 〃break〃 to the extent of four thousand feet。 Later； another fault occurred； which readjusted the displacement somewhat； and reduced the difference to two thousand feet； yet left the evidences of the former wide divergence。 It was also during these uplift periods that the volcanic mountains of the region came into existence； as the San Francisco Range； Mounts Kendricks； Sitgreaves； Williams and Floyd on the south； and the UinkaretsMounts Trumbull； Logan； Emmaon the north。
Lava Flows。 In one place； south of Mount Emma； Powell's party saw where vast floods of lava had flowed from it into the river。 They declare that 〃a stream of molten rock has run up the Canyon three or four miles； and down； we know not how far。 The whole north side； as far as we can see； is lined with the black basalt； and high up on the opposite wall are patches of the same material； resting on the benches； and filling old alcoves and caves； and giving to the wall a spotted appearance。〃 All these volcanic mountains can be seen from Hopi or Yavapai points； near El Tovar。
The Algonkian Strata。 The Algonkian strata of the Grand Canyon are by far the most interesting； Major Powell was the first to call attention to their existence in his report of explorations of 1869…1872； and he discusses their origin and history as far as was possible with the small amount of data he had at hand。 Later Dr。 Charles D。 Walcott； his successor as Director of the United States Geological Survey； and now the Secretary of the Smithsonian Institution； spent a full winter in the heart of the Canyon； especially studying the unique formations。 Unique they are； for； though found elsewhere on the earth； they are exceedingly rare； and； up to this time； had received little study and were unknown and unnamed。 The area studied by Walcott lies at the very entrance to the Grand Canyon； near where the Marble Canyon and Little Colorado Canyon join the main one。 While the series cross the river and are a fine feature of Red Canyon Trail； the main study was done on the north side。 Dr。 Walcott thus locates the site of his studies： 〃This area； between 35 degrees 57 minutes and 36 degrees 17 minutes north latitude； and between 111 degrees 47 minutes and 112 degrees west longitude； is in the valley portion of the Canyon； between the mouth of Marble Canyon and a point south of Vishnu's Temple； a little west of where the Colorado River changes its course from south to southwest。 It is wholly within the greater depths of the Grand Canyon； east and southeast of the Kaibab Plateau。 The intercanyon valleys of this portion of the Grand Canyon extend back from three to seven miles west of the river； and are eroded in the crest of the Monoclinal fold that forms the eastern margin of the Kaibab Plateau。〃
There are also interesting remnants of Algonkian directly opposite El Tovar to the west of the Bright Angel Creek。 They are