Plate VIII
PLATE IX
Plate IX. Photograph of a cast made by pouring plaster over a surface of mud in which ice crystals had formed, in Rock Island, Illinois, soon after the ice in the crystals had been removed by slow natural sublimation into the atmosphere, leaving open cracks in the mud. In the locality where this cast was made, the crystals were relatively slender, distant, and some gently curved, like those seen in [Plate V]. Slightly reduced.