A thick sequence of alternating bioclastic limestone and other clastic beds of Early Permian age has been steeply tilted, but the rocks appear to have retained their sedimentary structure, even in detail. Microscopic examination shows, however, that at many places the limestone beds have undergone intense plastic flow. Most of the calcite shells, except crinoid ossicles, have been attenuated beyond recognition. Each crinoid ossicle was secreted by the animal as an anhedral crystal of calcite and each contained a biologically imposed, cribriform lattice structure and such pores or external canals or processes as the biologic or skeletal function required. It is widely accepted that calcite crystals in marble are weak, but the anhedral calcite crystals in these ossicles sho astonishingly little deformation even where surrounded by flow lines of calcite shell material and the usual "shadow structures" in the low-pressure areas. The cribriform lattice and general form of many ossicles show some degree of warping and lamellar twinning in the crystal structure, but in all samples the crinoid plates were far more durable than any of the associated biogenic calcite.

Shells of Triticites and Pseudofusulina are present. Their well-known keriothecal wall structures serve not only as a measure of the extreme extent of attenuation locally, but also show that the plastic flow represents adjustments between particles of a fineness to and beyond the limits of visual resolution. Relatively little fracturing accompanied the deformation. Parts of a few fusulinid shells were agatized. The silicified parts of shells are undeformed, but the unsilicified parts are attenuated, showing that silicification preceded the plastic flow and that it can not have been a product of Recent exhumation and weathering. The adjacent igneous intrusions and associated deformation of these Permian beds have not yet been dated more accurately than Triassic to Miocene. Numerous exa ples of the greater durability of echinoderm ossicles than that of other calcite shells, even in environments of low-grade metamorphism, have been observed or reported, but the samples discussed here exceed by far any known differences in display of strength.

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