The specimen to which this paper refers, is one of a number of minerals from Kurdistan, presented to the Hunterian Museum, in Glasgow University, by Mr. D. Ferguson, to whom I am indebted for the following particulars of the occurrence. The exact locality is the Zarshuran River, in Kurdistan, where a large mineral vein, which has been worked for centuries for orpiment, is found. The country-rock is red sandstone, overlying, unconformably, altered slates and schists, which are intruded by a boss of felspathic granite or syenite. Near the surface the vein-stone is chiefly a kind of calc-sinter, but this disappears as the depth increases and calcite becomes the predominant mineral in the gangue, being associated with some quartz and fluorspar.