Excerpt from The Hollow Sperulites of the Yellowstone and Great BritainIn this instance the cavities of the Spherulite are related (a) to a ow - band, and (b) to the periphery of the spherulite.The lithophysae of Obsidian Cliff graduate into another common variety, distinguished by a porous structure and by the absence of a definite cavity. An entire absence of a cavity is, perhaps, rare, but it is not structurally important. Such forms may be conceived of as lithophysae in which the cavities have been distributed through the body of the spherulite and not localized or arranged in a definite way. These porous spherulites are irregular, lobate, or circular in outline: often the outer zone is harder and less friable than the central portions, and shows traces of a radial growth.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.

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