MODES OF OCCURRENCE. 
17 
dunite, and would make a sharp and nearly regular contact with the 
gneiss. The contact with the dunite would be in some places sharp 
and regular and in other places very irregular, and masses of the 
corundum would penetrate the dunite. In some cases there would 
Ic a somewhat gradual transition from the corundum to the peridotite, 
as represented in fig. 4. The rapid erosion to which rocks in a moun- 
D'unit< 
wmmm> ■ 
^mrn s 
! 
Il!: ;i 
^ a n 
ii - ,^. 
// ^> ; * 
^i i 
iWlli.i 
li%TB/-.? "ll=4l lilllr il 
ft - « II \ ,. ~g/*\ 
Hi' 
II 1 ! ' 
//.- #V '.* i Jl!!!i lll;'!l !| 
! I 
lull 
I 
I 
'■j*y- 
i'i 
ll! in 
GneissHlli 
III 
mi 
1 
i 
Ii 1 ! 
il 
mm P' 
II ».. 
I'^frJig llS'^ 11 
II 
ill 
i 
iiiiji 
l|l' l|! 
! ! i;i 
ii i ! i i 
n « 
* *■ <r, '/jil!| ! 
Ii =, 
// . i\ =•! 1 1 , 
l ' ■ I 
•11 
'Pl'.n 
* ^ 
;rV,\Siii!liillilii 
l!l|!;!!!'!l 
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I II 
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Hiii 
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iiiliiili 
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iHiiiinliilihilillm' 
a 
Fig. -t.— Ideal vertical cross section showing a somewhat gradual transition from corundum to 
peridotite. 
tain region are subjected would readily wear them down to their 
present condition, represented by the dotted lines in fig. 3. 
The corundum veins, I, II, and III, in fig. 3, which at the present 
time have no connection with one another, but are each separate and 
distinct, were at the time of their formation part of the corundum con- 
centrated along 1 the border of the dunite. Some of these veins would 
Bull. ISO— oi- 
