Macroscopic Characteristics

Cone-in-cone structures consist of cones fitting one into another (nested cones) arranged in lenticular beds of several decimeter thickness and width, in calcite-cemented sandstones, or at the edges of disc-like to ellipsoidal concretions several decimeters in thickness and up to about 10 m long, in shales (Fig. 2). The orientation of the cones is mostly vertical with apices directed downwards in singular cone layers (sometimes called "beef'), but subradial arrangements with apices pointing toward the core of a concretion have also been described. Individual cones range from less than 1 to about 12 cm in height. Cone apical angles vary from 12° to 100°, but most reported angles fall between 20° and 60°. Shorter cones tend to

Fig. 2. Schematic cross section of cone-in-cone structures found in shale: A) Individual layers in the Devonian of Pennsylvania (redrawn by Selles-Martinez 1994, after Gresley 1894), and B) ellipsoidal concretion, Canadaway Fm., Upper Devonian, Western New York; cone axes are perpendicular to bedding in surrounding shale and to the central layer, which consists of silt (simplified after Gilman and Metzger 1967).

Fig. 2. Schematic cross section of cone-in-cone structures found in shale: A) Individual layers in the Devonian of Pennsylvania (redrawn by Selles-Martinez 1994, after Gresley 1894), and B) ellipsoidal concretion, Canadaway Fm., Upper Devonian, Western New York; cone axes are perpendicular to bedding in surrounding shale and to the central layer, which consists of silt (simplified after Gilman and Metzger 1967).

have relatively larger apical angles.

The cones are separated by striated argillaceous films forming annular or anastomosing rings that are more common in shorter cones. These annular depressions filled by argillaceous material produce a ribbed or scaly appearance (corrugation) on the surface left by the removal of the cones (cone cups). Cone terminations are visible on the top of the layers, where cones commonly project out (telescoping of cones). Important characteristics of cone-in-cone structures are summarized in Table 1.

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