LOGAN: FREEZE-OUT HILLS OF WYOMING. 117 



the amount of the last-named substance. The degree as well as 

 the uniformity of the induration depend upon the conditions of 

 sedimentation and subsequent strati^^raphical relations. A homoo- 

 enous stratum of sand in the belt of induration is more favorable to 

 the agents of cementation than a heterogeneous stratum composed of 

 sand and clay, for the reason that the former permits the freer circu- 

 lation of solutions. Again, if the mineral in solution be silica the 

 presence in the rock of large quantities of quartz will favor deposition 

 of the sihca because of the affinity which causes one mineral to select 

 Its kind m deposition or recrystallization-a principle which is well 

 illus rated m the process of enlargement of crystals by metasomatism 

 The cnaracter of the cementing substance depends upon the char- 

 acter and solubility of the rocks through which the percolating waters 

 pass before reaching the zone of induration. If the surface rocks and 

 the superincumbent rocks be limestones or calcareous shales the ce 

 ment will be, for the most part, calcite. If the source of the descend 

 mg waters be marshes into which the surface-waters are bringing 

 soluable iron compounds, the cementing agent is very likely to be 

 some form of iron. If, on the other hand, the surface-waters and the 

 percolating waters find their courses in sandstone, quartzite, or other 

 quartz-bearing rocks, the sandstone will be cemented by silica 



The induration of these sandstones is a continuous process which 

 began with the deposition of the beds, and is still taking place It is 

 taking place not alone in the deep-seated zone, but also in the periph 

 eral zone of weathering. Depth of burial had its influence by brino- 

 ing the quartz grains closer together, and thus leaving smaller spaces 

 to be filled by the cementing substance. The stratum of .sandstone 

 which becomes indurated while deeply buried is not constantly in a 

 zone of underground waters, but is alternately in a zone of satura- 

 tion and m a zone of imbibition. While in the zone of saturation 

 the rock spaces are filled with water containing the cement in solu- 

 tion When, however, by a diminution in the supply of water, the 

 stratum is brought above the zone of saturation into that of imbibi- 

 tion, evaporation takes place, and the minerals held in solution are 

 deposited. 



Induration continues, however, even after the rocks have been up- 

 turned by orogenic movement and the overlying rocks removed by 

 erosion. In the zone of weathering, the ascending waters are bring- 

 ing up minerals in solution to be deposited as the water is evaporated 

 ihis form of deposition is very common in arid or semi-arid reo-ions" 

 In western Kansas, ascending waters passing through a bed of calca 

 reous shales have, in one instance, built up a cone twenty feet hio-h 

 V\ here the underground waters come to the surface in some of the 



