1895. ] NEW YORK ACADEMY OF SCIENCES. 83 
as inclusions in the orthoclase, it is itself almost invariably rich 
in them; in fact this very great abundance of inclusions is a 
characteristic feature of the rock. The larger ones are 
biotite, apatite and zircon, but smaller undeter minable ones are 
present in countless numbers. They are at times arranged 
in more or less parallel rows with their longer axes in the same 
direction. Some of the plagioclases exhibit what are e apparently 
inclusions of feldspar of different composition and with crossed 
nicols give the crystal a mottled appearance. They may be 
similar to those described by Hobbs,* but different in that the 
inclusions do not form a central core. 
The plagioclase is usually quite fresh, but in addition to 
kaolinization sometimes exhibits a dusty alteration product 
along the cracks and cleavages. Limonite also occurs as an 
infiltration. 
Orthoclase. This is much less abundant than the quartz or 
plagioclase. It occursin grains like the quartz. Though noticed 
FELDSPAR INCLUSIONS, IN ORTHOCLASE AUGE 
sparingly in most of the sections its chief occurrence is in the 
“ Augen” west of Mamaroneck. These are round or lenticular 
and .5-1 in. long, and are often Carlsbad twins. Sections 
show them to be crowded with inclusions of feldspar of 
two types. First, small ones of square or rectangular outline, 
with an extinction of 35°-40° and second, fragments of plagioclase 
polysynthetically twinned. The former have their sides more 
or less parallel. They do not extinguish at the same time as their 
#1 Cy 
