100 SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
GENERAL STRUCTURAL FEATURES. 
From the foregoing sections, necessarily more or less incomplete, the general struc- 
tural characteristics of the western Vermont and eastern New York slate belt can be 
grasped. The structure of the Cambrian slate mass, which usually adjoins the Ordovi- 
cian schist, is illustrated in sections VI and VII. There arc close folds, more or less 
overturned to the west, with eastward-dipping slaty cleavage obscuring the bedding. 
The folds are so close and the cleavage is so pronounced that the cores of adjoining 
synclines and anticlines are brought very near together, orthe anticlinal portions oi 
several adjacent folds do not appear. In the northern part of the Cambrian area 
quartzite beds are more abundant within the roofing slates than in the southern. 
Although the entire mass of slate and quartzite is in places thrown into folds so 
greatly overturned that their axial planes are nearly horizontal, yet the slate itself 
is less distorted in the direction of the cleavage than in the southern area, and the 
cleavage itself is also less perfect in the northern than in the southern. Series of such 
various folds form compound anticlines and these minor Cambrian anticlinoria alter- 
nate with Ordovician synclinoria overlying Cambrian ones in apparent but not real 
conformity. As the Ordovician areas consist of shales, slates, grits, and small quartz- 
ite beds, the beds being more heterogeneous, slaty cleavage is less prevalent, but the 
folds are also overturned toward the west (see sections I, II, V, VI, VII, PL XXII). 
A north-northwesterly strike appears in the Cambrian rocks about Blissville and 
again at Cedar Point (see map, PI. XX). Large beds of quartzite overlie the roofing 
slate and are typical of this portion (section III, PI. XXII). 
GEOLOGICAL AM) GEOGRAPHICAL DISTRIBUTION OF THE VARIETIES 
OF SLATE. 
The quarry maps, Pis. X X and X X I. show that the slate quarries situated within 
the Cambrian areas are generally very near to or not far from the edge of the OrdfJ 
vician belts. In some places (as in Pawlet, Wells, West Castleton) the Cambrian 
slates occur within 100 or 200 feel of the Hudson grits. This is the case in such a ; 
variety of situations that the proximity of the two format ions can hardly be explained 
by faulting. The Cambrian roofing slates are, therefore, regarded as occurring not 
far from the top of the Lower Cambrian series as exposed in this region and very 
near the overlying Ordovician. As the Cambrian belts are made up of numerous 
folds, generally close and overturned, the slate- also occur toward the center of the* 
belts, hut their stratigraphical position is still the same. The first place to look for 
the Cambrian rooting slates is near the Cambro-Ordovician boundary. Where the 
red slate occurs in close proximity to and on the wesl side of the ( Jambrian green and 
purple slates and the dip is easterly, as it usually is, the red slate may be found 
underlying the "sea green," "unfading green," or purple slates, and vice versa; on 
the eastern side of the Cambrian areas the green and purple slates of the Cambria! 
maybe found underlying the red of the Ordovician when both dip easterly. At: 
several points (Blissville, Eureka, etc.) away from the Ordovician boundary the rock 
which appears to immediately underlie the Cambrian slates is the Olive grit (A), one 
of the so-called "wild rocks" of the quarrymen. It is uncertain whether there may 
not be one or more beds of slate interbedded with this. The rock which overlies the 
Cambrian slate is either the Black Patch grit (C) or the Cambrian black shale (D)« 
or the Ferruginous quartzite and sandstone (E). Perhaps most generally there is a 
bed of limestone conglomerate or breccia, followed by black shales or slates (D), see 
page 94. These vertical relations are pretty well established. 
The areal relations of the "sea green" and the "unfading green" are not at sM 
clear. There is nothing as yet to show that the stratigraphical position of these twe 
varieties of Cambrian slates is not identical. It seems probable that, at the latitude 
