In a quartz crystal, slightly over 2¾ inches in length, which has been in my possession for many years, and was stated to come from Derbyshire (possibly Castleton), there is a curious white cirrous inclusion which describes a graceful feather-like curve, and consists of a series of nearly parallel lines of colourless and transparent to opaque snow-white grains, which, under the microscope, are seen to be at times well defined rhombohedra; but for the most part they present the appearance of thorn. bohedra which have been more or less eroded, and they are so ranged in lines that one rhombohedron lies with one pair of faces slightly above or below the corresponding pair of faces of the succeeding rhombohedron, thus giving the line a distinctly serrated edge.