Denver & rio orande westeRjST RotiTE. 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 effectuall}^ 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 is 

 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. 



