HUNTINGTON AND GOLDTHWAIT: THE HURRICANE FAULT. 247 
stood at least six hundred feet lower than now. If, however, the river 
had now cut down to as low a level as it then occupied, it ought to be 
equally well graded, but this is by no means the case. Accordingly we 
are justified in assuming a greater uplift than six hundred feet. Ina 
preceding section we have put this at one thousand feet as an average 
for the whole region north of the Shivwits plateau. In certain places it 
may have been greater. A study of the map (Arizona, Mount Trumbull 
sheet) shows that where the Virgin river cuts through the Virgin 
mountains ten or twenty miles southwest of St. George it flows in a 
precipitous canyon of very young aspect. The gorge is incised to a depth 
of fifteen hundred feet in a maturely dissected mountain mass from 
which the young valley is almost as sharply distinguished as the Colorado 
canyon is from its plateau. A conclusion based only on map study 
cannot be final, but we believe that future observation will show that 
parts of the St. George block have been uplifted over fifteen hundred 
feet. This fact has an important bearing on the recent displacement 
which we shall now discuss. 
The Later Faulting. 
In all the foregoing consideration of the earlier faulting, the prolonged 
erosion, and the lava flows we have been constantly obliged to refer to 
the later faulting, and have spoken of it as though it were a proved fact 
for which we had already presented the evidence. So much, indeed, 
has been said that it is here necessary merely to summarize the facts, to 
discuss the offset by which the displacement passes from the Hurricane 
to the Grand Wash faults, and to point out the bearing of these facts on 
the history of the Grand canyon of the Colorado. 
The displacement by which the Colorado plateaus were uplifted and 
by which the cutting of the Grand canyon was inaugurated began as a 
general uplift of the whole country. This is shown by the renewed 
dissection in the blocks west of the faults as well as in those east of 
them, proving that the former were uplifted with the latter, though 
to a less extent. Soon, however, the eastern portion of the country, 
which is now known as the Colorado plateaus, broke away from the 
western. Basin Range portion and was uplifted at a more rapid rate. 
The displacement between these two blocks, so far as we have studied 
it, consists of three parts: (1) the later Hurricane fault, (2) the Fort 
Pierce monocline, and (3) the later Grand Wash fault. The evidence 
of the two faults lies chiefly in numerous displaced lava shects. Some 
