DEcEMBER 6, 1918] 
finer grained types; from highly gneissoid to 
very slightly or moderately gneissoid facies; 
and from notably granulated to only mod- 
erately granulated varieties. The effect is to 
give bands or layers of varying composition, 
color, granularity, foliation and granulation, 
yet all clearly belonging to a single rock body. 
Such bands or layers usually vary in width 
from an inch to a hundred feet or more, and 
in length from a few feet or rods to a quarter 
of a mile. Banded structures of this sort are 
common throughout the Adirondack region, 
but it should be made clear that they are by no 
means universal. Large bodies of syenite or 
granite are often remarkably uniform and 
free from any notable variations or banding. 
Bands of amphibolite which, in many places, 
eause the syenite or granite (more especially 
the latter) to exhibit a very pronounced banded 
structure are not considered in this paper. 
These present some puzzling features and data 
regarding their significance ate now being 
gathered by the writer. Also, distinct in- 
elusions of various types of undoubted Gren- 
ville gneisses which, in the form of lenses or 
layers, in many places produce a banded struc- 
ture are not discussed except in so far as they 
throw light upon some banding of the syenite- 
granite which has resulted from magmatic as- 
similation of such inclusions. 
Of the many hundreds of observed examples 
of banded structures considered to be essen- 
tially the result of magmatic differentiation, a 
few will be described in order to give a proper 
conception of the more common and character- 
istic variations. 
On the mountain spurs, respectively one 
mile northeast and two miles east of White- 
house (Lake Pleasant quadrangle), there are 
shown many facies of the syenite-granite series 
ranging from greenish-gray hornblende syenite 
and granite syenite to gray and pink granite 
and coarse, almost prophyritic, granite. Such 
rocks play back and forth upon each other by 
sharp transitions repeatedly for a distance of 
one half of a mile on each mountain spur 
where the almost barren ledges are conspicu- 
ously banded in layers usually from a few feet 
to a few rods wide and parallel to the folia- 
SCIENCE 
561 
tion. These bands show many diffenences in 
foliation, granulation and granularity. Va- 
riations of this sort are perhaps the most 
abundant throughout the Adirondacks. 
By the road one and one half miles south- 
west of Long Lake village (Blue Mountain 
quadrangle) a freshly blasted ledge finely ex- 
hibits bands of greenish-gray syenite, granitic 
syenite, and gray granite. One band of light 
gray hornblende granite two and one half feet 
wide passes by insensible gradations into green- 
ish-gray pyroxene syenite on either side. The 
bands are parallel to the foliation which va- 
ries considerably. 
A hand specimen taken from a ledge by the 
lake shore near Adirondack village (Schroon 
Lake quadrangle) is distinctly foliated and 
granulated with a pink band especially rich in 
feldspar adjacent to a band very rich in quartz 
plus some garnets, these two bands having on 
either side gray granite consisting of quartz, 
feldspar, hornblende and some biotite. These 
very narrow bands, not sharply separated from 
each other, are parallel to the foliation. In 
the same quadrangle, one half of a mile north 
of Moxham pond, granite in a road metal 
quarry shows notable variations in coarseness 
of grain often within a foot or two. 
The red hornblende granite of the northern 
portion of the Port Leyden quadrangle often 
contains bands of gray quartz syenite in subor- 
dinate amount parallel to the foliation. Good 
exposures are by the lower road crossing on 
Otter creek. 
Professor Cushing, describing the granitic 
syenite of the Long Lake quadrangle, says: 
Much of the rock is alternately green and red, 
quite quartzose, and a rock distinctly intermediate 
between syenite and granite, often passing into 
granite. Much of it is uniformly red, and the rocks 
range from syenite to granite in composition.1 
Professor Kemp, in his description of the 
syenite of the Elizabethtown-Port Henry 
quadrangles, says: 
The most acidie variety will quite sharply re- 
place it (syenite); and in the same way a very 
basie variety may come in and constitute the sec- 
tion for 50 or 100 feet or more. Yet while the 
1N. Y. State Mus, Bul. 115, p. 478. 
