78 CORUNDUM, ITS OCCURRENCE AND DISTRIBUTION. 
bearing on the origin of the corundum that he undoubtedly had ii 
mind he does not mention in his article. Doctor Smith also state 
that he found " chrysolite attached as an enveloping matter to con 
siderable masses of corundum." He makes, however, apparently iv 
further mention of this occurrence in any of his writings. 
In a description of the " Jenks corundum mine " Mr. Ii. A^' 
Raymond ^ calls attention to the occurrence of transparent nodule 
of corundum in a matrix of the same material, and also of the grea 
variation in the appearance of the corundum from the differen 
veins. One of the veins has produced more of the gem materia 
while it contains but few large masses of the corundum. 
Mr. A. A. Julien, in a paper published in 1882,^ considers the corun 
dum in all cases a secondary or alteration product, and explains al 
the phenomena of alteration in the veins by the introduction of 
solution of soda and alumina into the fissures during the period o 
alteration and metamorphism, believing at the time that the peri 
dotite Avas of sedimentary origin. 
In an article commenting on Julien 's theory regarding the origi 
of the peridotites, Wadsworth,^ in speaking of the corundum, say 
that it is looked upon as a secondary mineral, and not, as Genth helc 
as the primary material from which many minerals originated. 
Mr. T. M. Chatard '^ made a very careful chemical study of tli 
material collected across the contact between the gneiss and tli 
peridotite at Corundum Hill. He points out as a result of his chen; 
ical analyses that, starting from the gneiss, there is a progressiv 
increase of magnesia in the vein material as the peridotite i 
approached, and that there is an approximate decrease in the pei 
centage of alumina. According to these analj^ses the series from tli 
section across the vein are divided into three groups — aluminui 
silicates, aluminum-magnesium silicates, and magnesium silicate; 
The middle term of this chemical series is also the middle numbc 
of the field series. He regards the corundum as an accessory minera 
frequently not being found at all in the vein and sometimes in bii 
small quantity, and therefore to be considered as the result of 
certain balance between the magnesium and the aluminum silicate 
which have by their union produced the chlorite and the vermiculite 
In describing the occurrence of corundmn in Chester County, Pa 
Mr. J. P. Lesley ^ says that it seems difficult to imagine its excessi^ 
compact hardness as produced in any other way than by heat. 
" Trans. Am. Inst. Min. Engs., vol. 7, 1879, 89. 
"Proc. Boston Soc. Nat. Hist, vol. 2, 1882, p. 141-149. 
'■ Science, vol. .3, 1884, p. 486. 
" Bull. U. S. Geol. Survey No. 42, 1887, pp. 45-6.3. 
« Geol. Survey Pennsylvania, C4, p. 352, 1883. 
