10 GUIDEBOOK OF THE WESTERN UNITED STATES. 
indication of the real structure of the mountain range. The streams 
have cut deep canyons, and many interesting views may be seen on 
the right of the train as it passes from branch to branch of South 
Boulder Creek, here crossing a canyon on a high trestle and there 
plunging into the darkness of a tunnel through a spur. Where 
South Boulder Creek is first seen it lies far below the level of the 
road, but its bed slopes steeply headward and is finally crossed by 
the railroad well above the sharp canyon, which represents the latest 
period of stream cutting in this region. If the trip is made in July 
the traveler may have the pleasure of seeing in the foothills acres 
of the beautiful Rocky Mountain columbine (Pl. IV, &), which has 
been adopted as the floral emblem of Colorado. The plant grows 
about 3 feet high, and each stalk bears a number of delicate lavender- 
tinted blossoms which become white as the season advances. 
The first large village above the point where the railroad crosses 
South Boulder Creek is Rollinsville. Here the traveler sees no sug- 
gestions of mining, but if he could follow for a distance of 4 miles the 
road that climbs the hill on the north (right) he would find himself _ 
in a district that furnishes the metal for the filaments of most of 
the incandescent electric bulbs made in this country. This metal 
is tungsten, and a small percentage of it is contained in the steel 
from which most of the modern machine tools are made. 
only and o dates 
reciica nti the gneisses are holo- 
crystalline [entirely crystalline] granu- 
are arranged in eS parallel 
Bees or layers. 
width and texture these sara 
vary “indetitely It is common to 
and oarsely yeaa 
quartz several sities in width, alter- 
nating with others of feldspar, or feld- 
rnblen 
é ent 
mica laminae [layers 
vary from finely and ‘prealy qutis 
through all grades of coarseness and 
ome at times so massive as to be 
indistinguishable in baud am speci- 
mens from granites. 
“The origin of elses 2 ae 
in many cases somewhat obscure, the 
banded or ified structure being con- 
sidered by some as representing the 
original bedding of the sediments, the 
different bands representing layers 0 
varying composition. This structure 
is now, however, besarigree to be due 
to mechanical causes and in no way 
dependent upon peer stratification. 
he name, as commonly used, is made 
Pe include rocks of widely Nae 
ucture, which are beyond doubt i 
nage sedimentary and in part aria 
in all ses altered from their 
s been 
brought about not by heat and cryntie 
lization alone, but in many cases by 
folding so comple 
od 
= fe the present state of our knowl- 
edge it is in most cases impossible to 
separate what 
ding and which may or may not be ~ 
altered eruptives. 
rant the SPER eon of she term knead- — 
may be true metamor- — 
phosed sedimentary gneisses from those _ 
in which the foliated or banded struc- 3 
ture is in no way connected with bed- . 
PS ae 
ee 
eg es 
