486 © Bibliographical Notice. 
eruptive forces were an event subsequent to the elevation of the 
metamorphic nucleus. This is shown in hundreds of instances in 
Southern Colorado and New Mexico, where the eruptive material is 
oftentimes seda out over the metamorphie rocks, concealing them 
over large area 
** All over ie mining-districts are well-marked anticlinal, s syn- 
clinal, and what I have called * monoclinal' valleys. Nearly all the 
little streams flow, a portion or all their way, through these mono- 
clinal valleys or rifts. In most cases the stream passes along the 
rift from source to mouth, but occasionally bursts through the up- 
heaved ridges at right angles, resuming its course again in some 
the mining-distri 
** In these bes are oftentimes aecumulated immense — of 
modern drift. Sometimes there are proofs that these valleys have 
been gorged for a time, and a bed of very coarse gravel and boulders 
will accumulate, hundreds of feet in thickness. Near Georgetown 
there is a fine example of this modern drift-action 
* It would seem that the valley of that branch ‘of Clear Creek in 
which the Brown and Terrible silver-lodes are located was gorged 
m e fin 
at one time, p es of e sand and 
coarse materials accumulated against the gorge, and at a subsequent 
period the creek wore a new channel through this material e 
upper side of this drift-deposit is fine sand, but the materials grow 
coarser as we descend, until, at the lower "ane there are immense 
irregular or partially worn masses of granite. On the sides of the 
valley the rocks are often mueh smoothed and grooved as if by 
floating masses of ice. We assume the position, of which there is 
most ample evidence all over the Rocky-Mountain region, that at a 
comparatively modern geological period the temperature was very 
South Platte, as that stream flows through the range east - Ras 
uth Park, shows not only these accumulations of very c 
boulder-drift, but when this drift is stripped off, the deste 
rocks are found smoothed, and in some instances scratched, as if by 
floating icebergs 
Dr. PRA regards the lignites nius agra into rds coal) of 
er; of little 
to 
for a id of 600 to 1000 miles in ev every dirdi there is little or 
no fuel either on or beneath the surface ;” and if these coals can be 
made useful for smelting the iron-ore abounding on all sides, and 
now reduced with charcoal, “ the future value of these deposits can- 
not be over-estimated " in exerting * the same kind of influence over 
