Hanging Valleys of Georgetown, Col. — Crosby. 45 
Randall, of Georgetown. For a length of a mile or more along 
the lower slope of the mountain the country rock is in a shat- 
tered condition, so that very little continuously solid rock is 
found, even at a depth of hundreds of feet, the structure being 
so open at some points as to permit a free circulation of air 
through the ground. Undoubtedly the fissure system and the 
veins antedate the modern escarpment, at least in the main; 
but that there has been comparatively recent movement along 
this line is unquestionable; and of this the unlithified selvage, 
and not uncommon brecciation of the vein contents, with depo- 
sition of cryptocrystalline secondary quartz, are evidence. 
There is evidence in the vein developments and in the 
breaks of the northwestern spur of Leavenworth mountain that 
the fissure system divides in this mountain, a more northerly 
branch following and defining the northern base of the moun- 
tain and thus determining the abrupt and square southern end 
of the Georgetown valley. A fracture system, which might be 
regarded as either a southward continuation or a repetition of 
the main Griffith-Centennial line, traverses the eastern slope 
of Leavenworth mountain. It is well exposed for study in the 
extensive workings of the Aliunde mine, and is seen to be char- 
acterized by a dike of porphyry, the geological recency of 
which is indicated by its broad margins of obsidian. The dike 
probably postdates the ore development, in the main, but the 
indications of movement subsequently to the formation of the 
dike -are also very plain; and the downthrow is here quite clear- 
ly to the east and not to the. west, although still on the side 
towards the valley. The chief topographic indication of this 
displacement is found in. the dislocation of the tributary valley 
of Argentine creek, which thus holds the relation of a hanging 
valley to the valley of Leavenworth creek. In this instance 
the creek has notched its escarpment less deeply and, falling 
several hundred feet in a small fraction of a mile, develops the 
water power utilized in the operation of the Aliunde mine. That 
the displacement at the foot of Leavenworth gulch is not meas- 
ured in its entirety by the hight of the escarpment, as shown 
in Figure 1, is proved by the fact that while the Dewey & 
Wheeler concentrating mill, which is the point of view for Fig- 
ure 2, stands on bed rock, which was blasted to prepare the 
foundation, a shaft about 100 feet from the mill, on the north 
