CORUNDUM TN IGNEOUS ROCKS. 49 
SomcAvhat similar to this is the occurrence of coriinchiiii in dikes of 
syenite which penetrate the gneisses over extensive areas of Hali- 
burton, Peterboro, Hastings, and Ilenfrew counties, Ontario, Can- 
ada. The corundum occurs in white or gray to bronzy crystals in 
the rock, varying from half an inch to 2 or 3 inches in diameter and 
from 1 to 4 or 5 inches in length. It is very variable in quantity, 
ranging from less than 10 per cent to 80 or 40 i)ei- cent of the rock 
mass. An average of 12 to 15 per cent has been reported from some 
localities. Besides corundum, the syenites carry small amounts of 
magnetite, pyrite, garnet, zircon, and sodalite. 
My attention was first called to this occurrence of corimdum by 
Prof. F. W. Traphagen, to whom I am indebted for the first specimens 
of this corundum sent to me. 
CORUNDUM IN PECxMATITE. 
Occurrences of corundum in pegmatite are extremely rare, but it 
has been found in this rock in Iavo localities in Haywood County, 
N. C. One is at Retreat, on Pigeon River, miles southeast of 
Waynesville, where corundum occurs in small pegmatite dikes, cut- 
ting the sa prolific, garnetiferous gneisses or schists. Accompany- 
ing these dikes are thin seams of vermiculites that also carry corun- 
dum. The other locality is 8 miles northeast of Canton, at the Pres- 
ley mine, Avhere corundum occurs in a pegmatite dike which intersects 
a mass of dark-green amphibolite. The corundum is found sur- 
rounded by both feldspar and mica. 
An interesting occurrence of corundum that has recently come to 
the writer's notice is in Fremont County, Colo., about 7 miles from 
Canyon, which is also the nearest railroad station. The corundum 
occurs In a matrix composed of quartz, plagioclase feldspar, and 
mica (muscovite and biotite). The maximum width of this rock 
that has been observed is 3 feet, and it has been traced for a distance 
of 3,000 feet. The corundum is thickl}^ scattered through the rock, 
and is in small particles and fragments up to half an inch or more 
in diameter. It does not occur in good crystals, but some rough 
hexagonal prisms half an inch in diameter were observed. Its color 
varies from nearly colorless through a pale bluish to a rather deep 
blue and to a pale greenish. There is but little development of part- 
ing planes in the corundum, and it shows on nearly all its exposed 
surfaces a rough conchoidal fracture. In the specimens that have 
been examined the quartz forms a considerable percentage of the 
rock, while the corundum sometimes appears nearly as prominent. 
The feldspars and micas are developed to a less extent. The corun- 
dum is transparent to semitransparent, and some is of gem quality. 
Bull. 269— 06 M 4 
