172 E. H. BARBOUR SAND CRYSTALS 



This is shown graphicall_y in figure 5, plate 18, which also shows the 

 deviation of Ifhe faces from the straight lines of the included polygon. 

 The rounded faces of the sand crystal correspond to the faces of the 

 scalenohedron blended into 6 continuous surfaces easily mistaken for 

 prismatic or pyramidal faces. The curved ends of these crystals offer 

 no more difficult}'^ than do the curved and warped ftxces. Almost every 

 scalenohedron is modified, and its ends visibly rounded by the combi- 

 nation of one or more sets of rhombohedral planes. An attempt is 

 made to show this graphically in figure 4, plate 18. These crystallo- 

 graphic signs are capable of exact interpretation by the crystallographer, 

 to whom they must be consigned for further consideration, the writer 

 contenting himself with this brief history of these remarkable new 

 crystals and their apparent relation to certain concretionary forms. 



