Al4 WEED AND PIRSSON 
6(010) according to Michel Levy’s method, and which show 
both albite and Carlsbad twinning extinguish nearly parallel to 
the plane of the nicols, the angles for all lamelle varying but a 
degree or two. The difference in illumination in the Carlsbad 
halves for such sections is consequently very small. The total 
amount of phenocrysts in proportion to groundmass is large. 
The groundmass is exceedingly fine-grained, microcrystalline, 
almost cryptocrystalline in fact; the great difference between the 
large phenocrysts and the fineness of the groundmass being one 
of the striking features of the rock. Examined with high powers 
it is seen to be composed of unstriated feldspar with a subordi- 
nate amount of quartz. The feldspar is turbid, apparently from 
leaves of kaolin. The fineness of grain together with the turbid 
character, and lack of contact lines between fresh feldspar and 
quartz prevents the satisfactory determination of the feldspar by 
Becke’s method or other optical means. We can safely conclude, 
however, from the analysis that plagioclase is not present and 
that it must consist mainly of orthoclase with some addition of 
the albite molecule, since the very small amount of lime must be 
entirely used up in the production of the oligoclase phenocrysts. 
An analysis by Dr. H. N. Stokes of the United States Geological 
Survey furnished the following results : 
SiO, - - : - - 68.65 
MlaOg  < - - - - - 18.31 
Fe,O, - ¢ - - - 56 
FeO 2 : = c - = .08 
MgO - - - = 12 
CaO . - - = - - 1.00 
Na,O 2 - - - = 4.86 
K,O - - - . - - 4.74 
Li,O - - = - = trace 
TO, - - - - - - .20 
MnO - - = - - trace 
BaO - - - - - - 5113} 
SrO - - - = - .10 
H,O above 110° = : - = gf) 
H,O below 110° - - - - 277 
Fl 2 a = - - - trace 
Cll - = = = ; : 03 
SOx c 2 - = - = trace 
P.O; - - - - - trace 
Total > - - = - 99.88 
The striking feature of this analysis is the exceedingly small 
