SOUTH DAKOTA SCHOOL OF MINES 57 



The first discovered and most noted locality is on Pine 

 Ridge Reservation at Devils Hill, near Corn creek, about 

 twenty miles south of White river. Concerning their oc- 

 currence here, Prof. Barbour, who has visited the locality, 

 says : "The mode of occurrence of these crystals seems most 

 unusual and remarkable. In a bed of sand scarcely three 

 feet thick, and so soft as to resemble the sand on the sea- 

 shore, occur these crystals in numbers which can best be 

 figured in tons. We dug them out with our bare hands. 

 They are mostly single crystals, with numerous doublets, 

 triplets, quadruplets and multiplets. In other words every 

 form from solitary crystals to crowded bunches and per- 

 fect radiating concretions were obtained. It was a matter of 

 special interest in the field to note that at the bottom of the 

 layer the bulk of these sand-lime crystals are solitary; one 

 foot higher there is an evident doubling of the crystals, 

 until within another foot they are in loosely crowded 

 clusters, a little higher in closely crowded continuous 

 clusters, pried out in blocks with difficulty ; still higher they 

 occur in closely crowded concretions in contact with one 

 another, making nearly a solid rock. A little higher this 

 mineralizing process culminates in pipes, compound pipes 

 and solid rocks composed wholly of crystals but 

 so solidified that their identity is lost, and is detected 

 only by a certain reflection of light, which differentiates the 

 otherwise invisible units by showing glistening hexagonal 

 sections. There could not have been a more gradual and 

 beautiful transition, and all confined to a bed six or eight 

 feet in thickness." 



The relation of the crystals to concretions, as indicated 

 above, discloses an important step in the development of 

 concretions in general, and doubtless to some such cause as 

 this crystallographic tendency is due the development of 

 all of the concretions of the Badland strata. 



Dikes and Veins. Dikes and veins are ordinarily 

 elongate, vertical, or nearly vertical rock or mineral masses 

 occupying fissures in a pre-existing rock. The filling body, 

 if intruded as an igneous rock while in the molten condi- 

 tion, is commonly referred to as a dike. If filled in by a slow 

 process of deposition from aqueous solution it is known 

 as a vein. It is now recognized that fissures sometimes 

 become filled with broken ( clastic ) material derived from 



