ORIGIN IN IGNEOUS ROCKS. 77 
stratum of chloritic rock (ripidolite) ; (5) tlio same, through which 
the corundum is reguhirly diffused, sometimes in narrow veins or 
widening out to several feet." Nowhere in this article does he suggest 
tlie probable origin of the corundum. 
Mr. J. LaAvrence Smith," in describing tlie occurrence of corundum 
nssociated with the peridotites of North Carolina and Georgia, spealvs 
of all the localities of corundum that he has observed or examined as 
exhibiting certain prominent characteristics conunon to all, but with 
each locality haAnng its own peculiar characteristics. He says that in 
all cases, hoAvever, the masses of corundum give evidence of having 
been formed by a process of segregation, Avhich he has described in a 
memoir ^ on the Asia ]\[inor emery, and that by the exercise of homo- 
geneous and chemical attractions the minerals which constitute and 
are associated with emery Avere separated out from the calcareous 
rock before it consolidated. 
Dr. F. A. Genth,^ although not touching directly on the origin of 
corundum or giving any evidence to sustain his statement, says that 
at the great period Avhen the chromiferous chrysolite beds Avere 
deposited a large quantity of alumina Avas separated, Avhich formed 
beds of corundum ; " that the corundum Avas subsequently acted upon 
and altered and changed into various minerals; that the ^'veins'' 
of chlorite, etc., are alterations of the original mass of corundum; 
and that the corundum might be found .in a less "altered or wholly 
unaltered condition Avlien the vein Avas explored below the action of 
surface influences. In speaking of the corundum crystals embedded in 
!the chlorite. Doctor Genth says the crystals " appear to have formed 
iifter a great portion of the original corundum has changed into 
^hlorite, as if there had been an excess of alumina ready for combina- 
tion, Avhich, not finding a supply of the requisite amount of silicic 
^icid and bases, had again crystallized as corundimi." 
i In an article on corundum and its associated rocks Mr. C. D. 
Smith '^ points out. but does not discuss, the facts that led to his 
belief in the igneous origin of the peridotites. He calls attention 
to the occurrence of corundum chiefly in chlorite veins and says: 
•' The chlorite seems to have been first crystallized ; and then the 
alumina, of Avhich the corundum is composed, was evidently in a 
state of solution and must have permeated the chlorite either in 
thermal Avaters or steam." The onh^ points given to sustain this 
theory are that plates or scales are sometimes inclosed in the corun- 
dum and that corundum has been observed that conforms in its faces 
and general shapes to the chlorite that is present. The other points 
«Am. Jour. Sci., 3d ser., vol. 6, pp. 180-186, 1873. 
f Idem, 2d ser., vol. 10, p. 354, 1850. 
'^ Proc. Am. Philos. See, vol. 13, pp. 3(51-406, 1873 ; Am, Jour. Sci., 3d ser., vol. 6, pp. 
461-462. 1873 (review). 
■^ Rept. Geol. Survey North Carolina, vol. 1, 1875, p. 91. 
