170 



E. H. BARBOUR — SAND CRYSTALS 



Apparently there were great amounts of the mineralizing solution in 

 sj^ots, and there the cr3'^stals continued to grow — a process which, if not 

 arrested, would have cemented the sand into a,mass of rock.. 



The sand element in these crystals, though forming nearl}^ 60 percent 

 of their bulk, ma}^ be considered an accident or as an inclusion, while 

 the lime element, which is the mineralizing agent, constitutes about 40 

 per cent, and is the cr3'stal proper. 



In the fine sand, in the coarse sand, and even in the pebbles, the cal- 

 cium carbonate, in cr3^stallizing out of solution, filled all the interstices 

 and interspaces with cement. The calcite is comparable in a wa^^ to the 

 connective tissue of the animal body ; dissolve all else away and yet the 

 form is preserved by a sponge of tissue ; remove the sand from the crys- 

 tals and the crystallographic form will be re[)resented by a sponge 

 of cementing calcite. When immersed in acid the cement is at once 

 attacked and the crystal quickly reduced to incoherent sand. 



Analyses 



The accompanying quantitative analyses were prepared by Messrs 

 PI G. Woodruff and Willis- Warner, assistants in the department of 

 geology of The University of Nebraska. The average of 4 crystals gives 

 63.81 percent sand and 36.19 per cent soluble matter. The concretions 

 and rock give nearly identical results. 



Average 



T.arge concretions. 

 Sand-crystal rock. . 



Average of four radiate sand-hnie con- 

 cretions, Sioux county 



Weijrht of 

 crystals. 



129.57 gr. 

 80.86 gr. 

 33.4 gr. 

 30.65 nr. 



Per cent 



of soluble 



matter. 



36.93 

 ;]().45 

 35.78 

 35.60 



36.19 



38.12 

 36.57 



41.11 



Microscopy and Crystallography 



Microscopic inspection, whether by transmitted or polarized light, 

 reveals little of interest save that the cementing calcite, while showing 



