On the topaz quartz porphyey or stanniferous elvan dykes of Mount Bischoff.

This rock was first described by S. N. Wintle in 1875 as eurite porphyry, which it had been termed by Professor G. H. F. Ulrich, who, however, did not publish his description until 1877. In 1875 also the late Chas. Gould wrote as follows : — " Mount Bischoff is a conical eminence rising to about 2,500ft. above the level of the sea. ... It consists of a small protrusion of a porphyritic rock having a felsitic base, with granules and crystals of quartz and felspar ; it weathers white, and is honeycombed or vesicular on the surface, most probably from the decomposition and removal of pyrites, which is freely disseminated throughout in places!." Includes photographic plates