PHeudomoi'phs from the Taconic Region. — Jlohhs. 47 
appeared to be composed mainly of a colorless mica and feldspar 
mottled by grains of quartz. The mica is in scales lying along 
the cleavage planes of the feldspar. Sometimes no feldspar 
could be made out with certainty, but the direction of the mica 
scales indicated clearly two cleavages nearly perpendicular, corre- 
sponding with those of feldspar, and in many cases the nodule 
was seen to be made up of two individuals simply twinned ac- 
cording to the Carlsbad or albite law, dividing the nodule in 
halves. These twins are oftentimes ver}' perfect, and closely 
resemble the simply twinned albite grains of Greylock mount- 
Appearance of nodules in thin section. M Silvery Mica, Q Quartz, 
FFibrolite. X 14. 
ain, except that they are larger and mainl}* composed of mica 
and quartz. 
Seen under the microscope in thin section, the nodules show as 
a background a network of colorless mica, possessing practically 
one orientation throughout the nodule (unless it is twinned), and 
inclosing quite uniformly distributed irregular areas of quartz. 
Penetrating the quartz and to some extent also the mica are 
numerous minute needles of filn'olite (See figure). No feldspar 
has been observed in section, yet many of the nodules doul)tless 
contain some residue of feldspar. On separating the rock pow- 
der in the Thoulet solution a large part of the mica was removed 
when the solution had a specific gravity of 2.8. Owing, how- 
ever, to the difficulty of making a perfect separation of the 
different constituents into homogeneous grains, the material con- 
tinued to fall in the solution until the specific gravity was some- 
what below that of quartz. As the specific gravit}' of the quartz 
