Barbour and Fisher — Caloite-Sand Crystal. 453 



crystal is obscured, and yet to the collector in the field, at 

 least, the identity is plain. The less obvious forms occur in 

 great masses and over wide areas, and pass for concretionary 

 sand. Their extent may be judged better from the fact that 

 they may be traced from the Indian Reservation of South 

 Dakota to northwestern and western Nebraska and eastern 

 Wyoming, as far w^est, at least, as Bates Hole, which is prac- 

 tically the extent of the Arikaree formation. Without a knowl- 

 edge of the actual sand crystals these obscure forms would 

 ordinarily be unrecognizable. In the case of the new forms as 

 in the case of the older ones they are the result of crystalliza- 



FiG, 3. Drawing of a crystal showing combination of acute and obtuse 

 rhombohedrons, the theoretical form of tlie actual crystal shown in figure 4. 



Fig. 4. Sand-iime crystal, natural size, type found west of Mitchell, in 

 the Chadron sandstone near the North Platte Eiver, on the Wyoming- 

 Nebraska line. 



tion in a sand bed saturated with water bearing calcium carbo- 

 nate in solution. The lime in crystallizing out followed some 

 one of the forms common to calcite and in the process cemented 

 the sand, together making a sand-calcite crystal. The crystal 

 proper is calcite. The sand may be viewed as an accident 

 incident to the crystallization of lime in a sand bed. A chem- 

 ical analysis shows that those from western I^Tebraska do not 

 differ essentially from those of South Dakota, as shown by 

 analyses of Mr. Willis Warner (Univ. Nebr. 1901). 



Analysis of Sand Crystals from Goshen Hole Region. 



Per cent Per cent of lime 



of sand. and soluble matter. 



Sand crystal 63-63 36*37 



Sand concretion 62-54 37'46 



Analyses of the above in full as furnished by Mr. Warner 

 are as follows : 



Crystal: silica, 49*32; phosphorus, -Oil; iron, Fe^Og-fAl^Og, 

 14-21; lime, CaC03, 33-27; magnesia, MgCOg, 3-14; undeter- 

 mined, probably manganese, '049. 



