34 FIELD CoLUMBIAN MusEumM—GEo.oey, Volt. III. 
which did not appear as cracks upon the surface of the section. The 
extinction was parallel to the principal cleavage, which hes in the 
plane of the axis of least elasticity. The index of refraction of this 
mineral was greater than that of the quartz. The cement throughout 
the entire slide was part of.one crystal with the growth of which the 
sand grains present had not interfered. This was indicated by the 
cleavage,. which was everywhere parallel with itself, and by the 
interference color which was the same hroughout the slide. The 
high specific gravity of the specimen and the presence of much barium 
sulphate, taken with the features shown in the slide indicate that this 
cement is barite. In this slide it was evidently cut parallel to m and 
showed the usual cleavage parallel to c and one set ‘parallel to m. 
An analysis of the specimens made in the Museum laboratories 
by the author gives the following result: 

nO ee oe PE cle Mees 50 fro 36.99 
Ba yi iy i oe Sisk sa a alee ae ere 3h 76 
SO re ere rer ne RT 19.20 
FeO ges EE oe 0 tet ee 0.82 
ALO een ne abtg hale = gy reac nen ee 5.36 
Cad fo oe FORGE Che be une aaee Ons 
MgO 2 Be bes 2 fA Siete eee eee 4 0.03 
HO 5 feck Lis ie cern eae ee 0). 27 
Organicy © 254 yh vey. Speers eae C233 
99.26 
This corresponds with a mineral composition (disregarding the 
silica required for the aluminous minerals) of: 
Barite\. 22 as eee 2 RE et ay Seer ee 54-42 
Quartz 8.0.5 OMA ne ee ae 36.99 
Miscellaneous’ wis s.70U ke ee 8.59 
2 
100.00 
From the analysis it would appear that some aluminous mineral 
is present bu: the slides fail to disclose such in quantities required to 
satisfy the analysis. Inasmuch as barite frequently contains 
similar elements as mpurities even when well crystallized, it appears 
best to provisionally include the minor elements in the barite for an 
approximate determination of mineral composition. The mineral 
composition thus becomes: 
Barité@es vnc). boy adds aie eee ee ee 63 
QuartKe vy ne An dan oe ee cy 
100 
This corresponds to a specific gravity of 3.77 against 3.380 
* From air-dried specimen, by Penfield’s method. 
7 Loss on ignition less water. 
