Macroscopic crystals of felspar are of common occurrence in the granitic area of Northern New South Wales and have been noted by various observers, but so far no crystallographic description has appeared. It is proposed in this paper to describe and illustrate some of the more interesting orthoclase crystals comprised in the Australian Museum collection, plagioclase felspars being reserved for a subsequent article. The specimens figured were with one exception acquired by the Trustees from Mr. D. A. Porter, of Tamworth, to whom also I am under obligation for particulars of their finding and mode of occurrence. Mr. E. 0. Andrews, of the Geological Survey of New South Wales, who possesses an extensive knowledge of the granites of New England, has been good enough to examine the collection, and has given me valuable information regarding the field relations of the rocks in which the felspars are found.