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CHALCEDONY-LIME NUTS FROM THE BAD LANDS.
ERWIN HINCKLEY BARBOUR.
During the summer of 1895, while in charge of the Morrill Geological Expedition, the author secured a number of the interesting chalcedony lime nuts found frequently in the miocene formation of the Bad Lands of the Hat Creek basin, Sioux county, Nebraska. These are closely related to the genus Hicoria. However, an examination of twenty-five to thirty specimens makes it apparent that they have characters sufficiently constant and distinct to constitute a new genus-Archihicoria. Although seen on former expeditions, this was the first time that specimens could be procured. Their color is light lavender, and their translucency and semi-transparency make them showy and attractive specimens. Besides, they are admirably preserved, and show half kernels, whole kernels, and even "double" parts. The last were veritable petrified philopenas. The kernels consist of lime and chalcedony so intimately related and associated together as to be indiscernible to the eye. However, by treating with hydrochloric acid the lime is dissolved, leaving a sponge of chalcedony preserving the shape of the kernel. It is probable that when these nuts were dropped in the water of the miocene lake, the kernel rotted away, but the shell, being tough and hard, would last for years under favorable conditions. Throughout the marls and clays of the Bad Lands there is a large amount of potash. This is dissolved by water, and then acts upon quartz, carrying it away in solution. This could find its way by infiltration into the interior of the nut. At the same time with this process the infiltration of water, carrying lime carbonate in solution, was going on, so that
doubtless the stone kernels consisting of pretty nearly equal parts of lime and silica, were deposited within the nuts. These kernels, of course, became hard and flinty in time and capable of resisting almost any amount of weathering. Not so the organic shell; this eventually would rot away, and so leave the filling, or kernel of chalcedony and lime. The author has already se
FIGURE 3.-A section of a chalcedony-lime nut, Archihicoria siouxensis, magnified three and one-half diameters, showing by the parallel lines chalcedony enclosing calcite.
cured six or eight of these; has examined some twenty-five or thirty in all; and has the promise of a large number besides. The finest specimens of this kind which he has yet seen showed each half of the kernel doubled and crumpled together, somewhat as one sometimes finds a double part in the modern hickory nut. Study will show that the so-called double part is a constant characteristic. Examination of section under the petrographic microscope shows beautifully the arrangement of the lime and chalcedony.
December 26, 1896.
PLATE V.-A group of chalcedony nuts, showing in the four vertical columns, four different aspects of each. Column 1 (to the left), front view of the embryo; 2, side view; 3, top view; 4, bottom view. Apparently the double part is the normal condition of all.