"The crystallographic orientation of optic axes, the crystallographic orientation of {0112} twins and the dimensional orientation of calcite from a drag folded vein are described. The external movements that have caused the deformation of the vein are interpreted and the fabric characteristics are related to them. The calcite fabric shows a marked similarity to those which have been produced experimentally. An analysis of the quartz fabrics demonstrates that there is no significant preferred orientation of optic axes." The specimens were obtained from the Pen y Glog slates, of Silurian age, collected from the Moel y Faen quarries in the Llangollen district, northern Wales. In the discussion, Nicholson takes issue on the time and intensity of the folding, on the amount of compression, and the local extent of vein fabric-forming conditions.

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