I'UVSICAI. CHAh'ACTKKS OK IIIK CONCRETIONS 1()7 



yaturatccl willi lime salts, which ci'y.stallized according to the laws gov- 

 erning calcite as far as interference ontlie part of the sand grains would 

 allow, and in so doing cemented together the grains into concretions or 

 l)i|)es and into compound pipes, making fairly solid rock of local extent. 

 A general view of radiate concretions, as well as concretionar}^ pipes, 

 ma}' he had in j)late 14, figures 1 and 2. The evolution of the radiate 

 concretion from the single sand cr3^stal is shown in j)late 15, figure 2. 

 Plate 16 shows the surface and inner structure of several radiate concre- 

 tions, figure 1 showing the surface and figure 2 the structure of a coarse 

 specimen ; figures 3 and 4 showing the surface and interior structure of 

 a finer form concreted around large pebhles. Figure 5 is an end view, 

 showing the radiate structure of the coral-like pipe seen in figure 2, 

 plate 14. Figures 6, 7, and 8 are small radiate concretions from Sioux 

 count}^ Nebraska. 



Material from Devil Hill Region 



But the most important light on this kind of development is given by 

 the strata containing the sand crystals, or concretion cr3^stals, as the 

 writer first named them in 1893, in the south-central portion of South 

 Dakota. Following the unbroken, sandy Arikavee north into South 

 Dakota, one soon finds it cut into ridges and solitary buttes, and disaj)- 

 pearing altogether within about 20 miles of the White river, one of the 

 northernmost remnants being Devil hill, situated between Potato creek 

 and Corn creek. Here, at an altitude of 3,600 feet (by barometer), on a 

 lofty, isolated hill of White River clay, rests a thin Arikaree cap. The 

 place bristles with grotesque erosion figures, ragged concretions, and 

 pil)es, together with loose sand and countless sand crystals so geometric 

 in design as to attract the notice of the early Indians, who considered 

 them supernaturally wrought for their destruction. Mingling our super- 

 stitions with theirs, they called the place Devil hill, a spot still viewed 

 with unnatural dread and discreetl}^ avoided. 



The region is distant from railroads, and the collector who would visit 

 this spot must plan for a trip, by team, of 3 or 4 days. Ranches owned 

 by Indians are some 20 to 25 miles apart, but all necessary comforts and 

 some luxuries can be secured in these Indian homes at a very reason- 

 able rate, and the trip may be made with comfort. A guide is necessary, 

 as the locality is remote, and it is often difficult to obtain satisfactory 

 information from the natives. 



The unique sand-lime crystals found exclusively in this spot, as far as 

 known, are hexagonal barrel-shaped forms with rounded terminations. 

 These were first made known to the writer in 1893 by the Reverend R. T- 



