DENVER & RIO GRANDE WESTERN ROUTE. 89 
in the form of calcareous tufa, building up domes of this material 
around the springs. A rather large spring of this kind is being 
utilized at Wellsville as a bathing pool, making it a general pleasure 
resort for the surrounding towns. 
Long ago, when the river was flowing at a much higher level than 
it is now, large springs issued along its banks much as the springs 
issue along its banks to-day, and they built up immense masses of 
tufa, which now stand several hundred feet above the railroad. This 
tufa consists of nearly pure carbonate of lime, and it is now being 
quarried in a large way for use in refining beet sugar and as flux in 
iron furnaces. 
West of Wellsville Springs the sides of the valley become steeper 
and the railroad is crowded to the bank of the river under a high cliff 
of Leadville limestone, which is the lowest formation of the Car- 
boniferous system. The beds of rock in this cliff have been greatly 
distorted by folding and in places stand nearly vertical, but the 
bedding has been largely obliterated by the solution and redeposition 
of the lime, so that the structure can not be determined from the 
train. After passing the great bend of the river to milepost 210, the 
synclinal structure may be plainly seen in the bluff on the far side of 
the river. 
The limestone is conspicuous on both sides of the valley almost to 
milepost 211, where it rises and disappears in the tops of the hills. 
It is underlain by thin-bedded quartzite, the age of which is not defi- 
nitely known, though it is considerably older than the other sedimen- 
tary rocks which the traveler has recently seen. The quartzite is so 
much changed by movement and pressure in the crust of the earth 
that at first sight it may not be recognized as a sedimentary rock. It 
is cut off in a short distance by a great mass of intrusive rock, which 
occupies a large area on the northeast side of the river valley and 
extends up the river as far as the stockyards 2 miles below Salida. 
Beyond this place the intrusive rocks are restricted to the northeast 
side of the river, or if they occur on the other side they have been 
dropped so low by faulting that they are effectually concealed by 
the gravel in the bottom of the valley. The Arkansas Valley above 
Salida has doubtless in many places been affected by faulting, so that 
large tracts have been dropped hundreds and possibly thousands of 
feet and the depressions so produced filled with sand, gravel, and 
boulders brought down from the great Sawatch Range on the west. 
About Salida in particular the evidence of such a dropped block 
Seems to be conclusive, for the river a few miles below the town 1s 
flowing on bedrock and it would still be running on or near bedrock 
at Salida had the bedrock not been depressed below its original level. 
