evidp:jncbs op the great erosion. 
71 
the base of each terrace clitf the inclination becomes a maximum.* This 
prolonged downward tilt towards the north must be borne in mind always 
in the attempted restoration of the platform to its original condition. 
Resuming’ the reconstruction, we begin at the Markdgunt Plateau. 
Here we find brackish and fresh water beds of Eocene age between 10,000 
and 11,000 feet above the sea. To find their position at the beginning of 
Tertiary time we must in imagination depress them that amount This car- 
ries down the Carboniferous nearly 12,000 feet below sea level. The same 
treatment is applicable to the entire front of the terraces as far as the Kai- 
parowits and indefinitely beyond. So also along the line of the Echo Cliffs 
as far south as our knowledge extends, with, however, a notably diminished 
amount in that direction arrising from the smaller thickness of the Mesozoic 
strata. Turning to the littoral belt in the Pine Valley Mountains we must 
depress the country between 4,000 and 6,000 feet, but in a very irregular 
way, because this region is greatly disturbed. We must also carry on this 
treatment southward along the Glrand Wa-sh and Virgen Range (Atlas Sheet 
II) as far as the Colorado. Reducing the Grand Wash fault in conjunction 
with this imaginary depression we find that the Carboniferous at the mouth 
of the Grand Cation goes 10,000 feet below the sea. The entire western 
edge of the Sheavwits goes with it. Along the Echo Cliffs the depression 
of the same horizon would be 7,500 feet below the sea, and would carry 
with it the Marble Canon platform, by the reduction of the Echo Cliff 
monocline. 
Thus around the greater part of the periphery of the district the recon- 
struction depresses the Carboniferous 7,500 to 12,000 feet below the sea. 
That the whole Grand Cation platform follows it seems incontestable. Any 
other reconstruction would force upon us some unknown arbitrary configu- 
ration of the Carboniferous strata for which there is no evidence. It is in- 
admissible to sujDpose that flexures, faults, or broad distortions once existed 
there which have subsequently been smoothed out or reset without leaving 
a single visible sign ; and any other reconstruction than the one here adopted 
would, it appears to me, involve just such assumptions. And they could 
*I caauot refrain from suggesting that this may be due to the gross weight of the terraces them- 
selves. It seems analogous to the action of creeping in deep mines. The inferior beds might have 
risen higher, were it not for the sudden intervention of these heavy masses of the terrace platforms. 
