Plate X. Photograph of a cast made by pouring plaster over a surface of
mud in which ice crystals had recently formed, in Rock Island, Ill., and
where they had later been removed by natural sublimations into the
atmosphere, leaving open cracks in the mud. It will be seen that the
crystal growth in this case involves an x-like or radiating pattern
formed of relatively very slender forms that almost everywhere are very
gently curved somewhat reminding of the slender thread-like crystals
sometimes seen in frost on windows. I have not yet seen any similar
fossil crystal growths as slender as these. Slightly reduced.
[Illustration: PLATE X]