90 SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
State, and has been extensively worked at Northlield, in Washington County. Th 
most important district, which furnishes the well known "green" and " purple : 
slates, lies between the Taconic range and Lake Chaniplain, extending from th 
town of Sudbury, in Rutland County, southward to Rupert, in Bennington Count} 
a distance of 26 miles. This belt also passes south-southwest into Washingto: 
County, \. Y., where, however, it has thus far proved of less economic importance 
The fourth is black slate, as yet undeveloped, and covering only from 10 to 1 
square miles in the town of Benson, in Rutland County, near Lake Chaniplain. 
NORTHFIELD. 
Geological relations. — The Vermont geological map" represents a belt of clay slate 
from 1 to 7 miles wide, as extending from Lake Memphremagog along the east sid 
of the Green Mountain axis as far south as Barnard, in Windsor County, a distanc 
of 90 miles. A recent paper and map by Richardson 6 represents a portion of thi 
slate belt 52 miles long, extending from North Calais, in Washington County, to 
point in Windsor County nearly 10 miles west of White River Junction. The ag 
of tins slate formation was thought to be probably Devonian by the authors of th 
older report, c but Richardson regards it as Lower Trenton. Conclusive paleontc 
logical evidence on the subject is yet lacking. ' 
This slate has been ([iiarried at Montpelier and Northheld, which are 10 mile 
apart. The strike of bedding at both places ranges from N. 10° to 20° E. At th 
Vermont Black Slate ( lompany's ouarry, 2 miles south of Northlield, the beds occu 
in minor very acute !'.>Ms, as shown in fig. 11 which strike N. 10° E., while the clea\ 
age, with an almost identical strike, dips W. at 75°. This indicates that the ger 
eral course of the bedding is not far from horizontal and that lateral repetitions e 
strata are to be looked for. The interpretation given by Richardson of PI. XV i 
his paper, referred to above, requires corroborative microscopic evidence. The kr 
easterly (by error printed west i dipping planes resemble a secondary cleavage, whil 
the steep westerly ones have the characteristics of bedding. 
The slate continues about 300 feet west of this quarry, and about a third of a mil 
east, making its total width in that vicinity about 2,000 feet. The general relatioi 
of this slate on the west are these: The western part contains a bed of novaculite u 
to 12 feet thick, and is followed by slate of no commercial value, which is followe 
at the foot of the range, about three-fourths mile southwest of the village, by 
sericite-chlorite-quartz-schist with grains of plagioclase, with a vertical slip cleava^ 
striking about north and a plicated bedding with a northerly pitch. Aftera covere 
interval, at a point on the range 2 miles west of the village, there is a large exposui 
of thin-bedded, more or less muscovitic quartzite (with grains of zircon anel plagi< 
clase), so intricately folded a- to strike N. 20° E., N. 20° W., N. 50° E.,andN. 90° II 
An area of a few acres of muscovite granite (formerly quarried, Moses King pro] 
erty) lies within this quartzite, or at least with this quartzite on both its east an 
west sides. This granite in places becomes orbicular, (tarrying nodules of concei 
trically arranged mica an inch in diameter.^ 
Northfield slate. — In 1904 but one quarry was in operation at Northlield, that of tl 
Vermont Black Slate Company, which measures about 100 feet along the strike, ( 
feet across it, and 55 feet in depth. The relations of cleavage and bedding are show 
in fig. 11. The cleavage strikes N. 12° E. and dips 75° W. Strike joints stril 
N. 15° E., dip 50° W., dip joints N. 77° W., and dip 85° S. Diagonal joints stril 
N. 55° E. and dip 05° NW. The grain dips 70° N. An exceptional false cleava^. 
dips 15°-20° N. As there are no ribbons in the bedding nor horizontal joints cros- 
"Hitchcock and Hager Rept. Geo]. Vermont, vol. 2, 1861, PI. I, p. 794. 
b Richardson, C. It.. The terranes of Orange County, Vi.. Slate, |». 77-71), and map, Pis. IX. I X.I. 
Rept. State Geologist Vermont, (3) of new series, 190i-1902. 
'•Vol. 1. p. 197. 
rfRept. Geol. Vermont, vol. 2, pp. 563, 564. 
