304 The American Geologist. *^^^'' i^*^*- 
close-grained red sandstone of the Permian is brought by fault- 
ing to the level of the Carboniferous strata of the lowest local 
horizon. No mine tunnel has penetrated the ore-bearing strata 
of this area and it is fair to presume that the dislocation is sev- 
eral hundred feet. It is, in fact, hard to tell what should be 
called the "great fault" referred to by M'r. Johnson's critic, for 
it would be fair to presume that by this is intended the fault 
following the crest of the range. But the crest is uneven and 
many different faults occupy that position. The entire lime belt 
crosses the range to the south, being thrown east by the uplift 
of the andesyte crater at the head of Hop cafion. It may be 
followed for miles into the heart of Water cation, where it still 
preserves the distinctive type of mineralization though impreg- 
nated with gold in the neighborhood of the andesyte, so that 
lead ores that in other parts of the camp carry only a little sil- 
ver, here occasionally bear one or two ounces of gold and con- 
siderable silver. 
In the centre of the lime belt, where the structure may be 
said to be quite typical, there exist lime beds to the east of the 
axial fault which are displaced over three hundred feet, ad- 
hering to the eastern slope and separated from the main body 
on the west by an interval of granite, indicating a still greater 
dislocation. 
To the north of the range, where the erosion has been more 
active, there are places where there remain only a few hundred 
feet of lime at a high angle and representing only about one 
hundred feet in thickness of the original lower (ore-bearing) 
strata, imbedded in granite and surrounded on all sides by it. 
The phenomena of "differential weathering" referred to 
are, indeed very beautiful and are worthy of special interest 
because they illustrate a fact, often overlooked, which may be 
called a "law," namely, that, where soft strata are faulted and 
left on a slope, the escarpment tends to move from the fault 
plane and, in the case of strike faults, particularly, the move- 
ment will be considerable and down-hill. 
The explanation of this is not far to seek. An escarpment 
facing the slope (i.e. east in the Magdalenas) is met at its base 
by a slope in the opposite sense. The waters flowing down the 
back slope encounter, in the trough, the edges of the strata, 
while the waters (less abundant as a rule) from the escarpment 
