A PRE-TERTIARY NEPHELINE-BEARING ROCK: 
WHILE engaged in a petrographical study of the glacial drift 
bowlders in the neighborhood of Columbus, Ohio, with a view to 
ascertaining their possible source, a bowlder of unusual interest 
was noted. It is related to types which have only recently been 
described in this country. The rarity and interest of the type 
and the hope of making possible its future identification with an 
occurrence found in place seems to justify a special description 
of this bowlder. Only a single specimen was found. This was 
about a foot and a half in diameter, with a surface weathering 
conspicuously rough and brown. 
Macroscopical characters—On the fresh fracture the rock 
shows a dark gray, compact, aphanitic groundmass, thickly 
studded with lath-shaped or, more rarely, tabular crystals of a 
triclinic feldspar. These phenocrysts have an average length of 
half an inch, but may be more than twice that length. They are 
white to colorless and translucent, with a pearly luster, and show 
the striations due to polysynthetic twinning, Upon the weathered 
surface of the rock they stand out in marked relief and are an 
opaque white, with a chalky texture. 
Less conspicuous, but distributed in great abundance through 
the rock, are groups of broadly rectangular, or hexagonal, white or 
nearly colorless crystals. These crystals do not exceed two milli- 
meters in diameter and are uniformly and clearly distinguished 
from the feldspar by their shape and size. They are not in 
marked relief on the weathered surface, but are conspicuous as 
small, squarish, chalky white spots. 
A dark-colored, ferromagnesian constituent, presumably 
augite, is present less conspicuously, as a phenocryst. Magne- 
tite can also be detected, and doubtfully olivine. 
Microscopical characters—The microscope shows the essential 
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