130 
G. T. PRIOR. 
Kersantites. 
The twenty-yards-wide dyke (579) cutting the crystalline limestone at Gj in the 
Northern Foothills [see p. 27) is an augite-biotite-kersantite. It is a speckled gray 
rock showing to the naked eye numerous flakes of biotite. Under the microscope 
irregular pale-green to pale-purple augites and much biotite in shreds and straggling 
ophitic patches are seen in a medium-grained mesh of plagioclase-laths with a little 
interstitial quartz (see Plate IX, Fig. 4). A little reddish-brown hornblende of the 
same character as in the preceding rocks is also present. The felspars are altered and 
kaolinised ; some with refraction less than that of Canada balsam are doubtless 
orthoclase, but most have higher refraction and are probably oligoclase. 
A chemical analysis of this rock gave the following result under I. For com- 
parison is appended, under II, an analysis of a kersantite from Stengerts, Spessart,* 
and under III that of a shoshonite from Beaverdam Creek, Yellowstone Park.f 
I. IA. II. III. 
(Northern Foothills.) Mol. ratios. (Stengerts.) (Beaverdam Creek.) 
SiO, 
50-71 
•840 
51-80 
53-49 
TiO a 
2-71 
•034 
0-71 
A1,0., 
17-08 
•107 
10-65 
17-19 
Pe.jOj 
1-38 
•009 
4-93 
4-73 
FeO 
8-71 
•122 
2-14 
3-25 
MnO 
o-oo 
0-2!) 
0-14 
CaO 
5’75 
• 102 
7-35 
0-34 
MgO 
3 • 03 
•090 
0 ' 90 
4-42 
Na,0 
3-82 
•001 
3-08 
3-23 
K..0 
3-03 
•037 
4-05 
3-80 
PA 
0-57 
•004 
0-43 
H.,0 at 110° = 
o-io 
11,0 above 110° = 
1-75 
S 1,32 
2-17 
CO, 
trace 
0-50 
BaO = O'OO 
99-99 
99-61 
100-02 
The Osann formula of this rock is : — 
®B9'66 G / [2 
which is near that of the shoshonite from Beaverdam Creek : — 
s oo a Cs| fia ^s a 
Calculation of the “norm” gave the following result:— 
KAlSi s O a 
= 
20-57 
NaAlSiA 
31-90 
CaALSiA 
= 
18-03 
CaSi0 3 
= 
2-67 
FcSiOj 
= 
1-45 
MgSiO, 
= 
1-20 
* Goller, Die Lamprophyrgiinge des siidlichen Vorspcssart. Neues. Jalirb., 1889, Beil.-bd. vi, p. 566. 
f Iddings, Geol. of the Yellowstone National Park. Monogr. U. S. Geol. Surv., 1899, No. 32, Part ii, 
p. 340. Analysis by Dakins. 
