BULL. GEOL. SOC. AM. 



VOL. 12, 1900, PL. 16 



FlCURE 1. — fiROVI»S OF SaND CONCRETION'S 



1 to 5 from Devil Hill ; •'., 7, 8, from Nebraska 



Figure '2.-Ci,ustkr m- Siikak (uyst.m.s (Fkjukk 1) and Intkki'knk.tuation Twins (Fiucrk 2) 

 SAND CONCRETIONS, SHEAF CRYSTALS, AND INTERPENETRATION TWINS 



