452 JBarhour and Fisher — Calcite-Sand Crystal. 



those exceeding 15 inches (28^°^).' The average crystal, of 

 which there are myriads to be dug out of loose sand, has a 

 length of two and one-half to three inches (H to 8''"'). (See 

 figs. 1 and 2, which are somewhat reduced.) Tliey are barrel- 

 shaped with rounded ends, and have been described by Penfield 

 and Ford"^ as hexagonal pyramids, but to the writers a study of 

 the form of the faces and a measurement of the angles seeais 

 to show that they are a combination of scalenohedron and 

 rhombohedron. 



Analyses. — Analyses of four crystals were made by Wood- 

 ruff and Warner, who determined the average percentage of 

 sand to be 63"81, leaving 36*19 soluble matter, as shown in 

 detail in the accompanying table. 



Per cent of 

 Weight of Per cent soluble 



crystal. sand. matter. 



CrystalKo. 1 129o7s'' 63-07 36-93 



" " 2.._ 80-36-'^ 63-55 36'45 



" '^ 3 33-40S'- 64-22 35-78 



" " 4 30-65S'' 64-40 35'60 



Average of the above 63-81 36-19 



Large concretions . 61-88 38-12 



Sand cr^^stal rock . 63*43 36-57 



Average of four radiate sand-lime con- 

 cretions, Sioux County, Nebraska.. 58'89 41-11 



Crystals from Goshen Hole Region, Wyoming. 



The new crystals, which also consist of sand cemented by 

 calcite, are very similar in color, texture, and in general appear- 

 ance to those from Washington County, South Dakota, differ 

 from them in being a combination of acute and obtuse rhom- 

 bohedrons. They show greater uniformity of size, varying 

 but little from one and one-half inches (IrO™"^) in length, by 

 seven-eighths inch (21°"^) in thickness (figs. 3, 4). Apparently 

 they occur much more sparingly than the others, although the 

 field remains to be fully explored. 



They show the same tendency to become doubled, clustered, 

 concretionary, and massive to such an extent that descriptions 

 already written of the one kind serve well for the other. If 

 the crystals happen to be particularly small, the size of the 

 sand grains is relatively so large that the exact outline of the 



* Penfield and Ford, Siliceous Calcites from the Bad Lands, Washington 

 County, South Dakota, this Journal, vol. ix, 1900, pp. 852-4, 1 plate, 4 

 figures. 



See also Barbour, Sand-Crystals and their relation to certain concre- 

 tionary forms, presented before the Geol. Soc. of America, Dec. 27, 1900, 

 printed in Bulletin of the Society, vol. xii, pp. 165-172, pis. 13 to 18, April 

 16, 1901. 



