42 CORUNDUM^ ITS OCCURRENCE AND DISTRIBUTION. 
mine are found to contain the various mineral components of the 
norite, i. e., hypersthene, feldspar, biotite, and garnet, no corundum 
having been observed here. 
This gradual transition of the pleonaste and iron ore into the nor- 
mal norite and the occurrence of the norite minerals in the compact 
ore are strong evidence that these ore bodies were formed by the dif- 
ferentiation of the molten norite magma. 
In the vicinity of these norites there are small masses of peridotite, 
but no corundum has been found associated with them. 
Fragments of mica-schist included in the eruptive are altered into 
a great variety of metamorphic minerals arranged in more or less dis- 
tinct zones. Beginning at the exterior, these zones consist of corun- 
dum and pleonaste follow^ed by quartz with magnetite, pleonaste, 
zircon, apatite, sphene, garnet, tourmaline, and many others. 
Very similar to the spinel emery of the Cortlandt norites are the 
occurrences of granular corundum and spinel in the basic aggregates 
of gabbros at Frankenstein and Veltlin, Germany, referred to on 
page 63. 
CORUNDUM IN PLUMASITE. 
An interesting discovery of corundum was made in Plumas County, 
Cal., about 1| miles northwest of the Meadow Valley post-office, by 
Mr. J. A. Edman, of Meadow Valley, and to him belongs the credit 
of the discovery of this new locality and new occurrence of corundum. 
The corundum -bearing rock was observed on the eastern and lower 
flank of Spanish Peak at an elevation of about 4,100 feet, and about 
2 miles due east of the summit and near the southwest margin of a 
broad belt of peridotite. The first specimens of the corundum were 
found by Mr. Edman as float in an adjoining gulch, and he traced it 
to its source. The corundum rock is composed of about 84 per cent 
of oligoclase and 16 per cent of corundum. The latter is in crystals 
varying in size from a fraction of an inch to 2 inches in length and 1 
inch in diameter. The general form of the crystals is pyramidal, due 
to acute rhombohedrons. There are but few of the crystals, however, 
tJiat are well defined, and in most cases they are imperfectly formed, 
and the faces are rough and corroded. There has been some altera- 
tion in the corundum crystals, which is apparent when these are 
broken, and on the fractured surface are observed small scales of 
a pearly mica, the laminae of w^hich are brittle. This has been deter- 
mined by Prof. A. C. Lawson to be margarite. 
Professor Lawson « lias made an examination of this occurrence of 
corundum, and states that there occurs through the feldspathic part 
of the rock a secondary mineral similar in appearance to corundum 
" Bull. Dept. Geol. Univ. Califoruia, vol. 3, No. 8, pp. 219-229. 
