Page:A Voyage of Discovery and Research in the Southern and Antarctic Regions Vol 2.djvu/29

] with aluminous earth in the strata of the same kind at Eagle Hawk Neck; particularly the butterfly shell, as it is called, upon the spot. The siliceous fossils of this genus are almost all imperfect, but do not bear marks of attrition: the contained animals are as completely fossilized as the shells. Their structure, which is curious, may perhaps be as fully demonstrated from these as by living specimens. The shell of the butterfly appears to be a trivalve, the third valve of which is rarely found attached. It is a kind of stalk, by means of which the animal seems to have been fixed to the rocks. The butterfly shell is not so plentifully distributed in the indurated clay rock at Point Puer as it is at Eagle Hawk Neck. The siliceous petrifactions abound in specimens of agate, chalcedony, cornelian, semiopal, and milky quartz; and in druses containing crystals of quartz, chiefly pellucid and amethystine. Pieces of granite, basalt, hornstone, siliceous and fossilized wood, &c., are found in the rock; but these are not so plentiful, nor, generally speaking, of so large a size as at Eagle Hawk Neck; the rock is also softer, being less impregnated with siliceous admixture. It is a breccia, consisting of an impalpable aluminous deposit, which, during its precipitation, has involved substances of various kinds, and remains terrestrial and marine. It contains numerous holes, such as would be formed by the entombment and subsequent decomposition of vegetable and animal forms. I once thought I could trace out the bed of a hawksbill turtle; and roots reduced to carbonaceous and fossilized states