62 SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
slate beds range only from 4 inches to 2 feet in thickness and the quartzite beds vary 
considerably. The entire thickness explored here thus measures from 327 to 342 
feet, and in that thickness there are no indications of duplication. This quartzite is 
usually very fine grained, and under the microscope proves to be biotitic and pyritif- 
erous, with a little magnetite and mu^'ovite and a few grains of zircon. In order to 
convey an idea of the great irregularity of the interbedding which marks the entire 
belt the following measurements of the Pond quarry series at the north edge of 
quarry are here given: 
Sectio?i <if Monson P<>n<I <jn<rrri/, Monson, Me. 
[Furnished by the courtesy of Mr. V. II. Crane, superintendent.] 
Feet. Incites. 
Slate 7-18 
Quartzite 6 
Slate 1 8 
Quartzite 2- 8 
Slate 1 10 
Quartzite 8 
Slate 2 
Quartzite 3 
Slate 4 
Quartzite 1 6 
Slate 4 
Quartzite 8 
Slate 4 
Quartzite 6 
Slate 15-18 
Quartzite 4 
Slate 5 
Quartzite 1 4 
Slate 7-8 
Quartzite 4 
Slate 3 
Quartzite 1 2- 4 
Slate 3 
Quartzite 8-12 
Slate 8 
Quartzite 20 
Slate 7 
Quartzite 2 
Slate 6 
Quartzite 11 
Total slate, 79-93 feet 6 inches. 
Total quartzite, 48 feet 5 inches to 49 feet 5 inches. 
There is sometimes a transition from the quartzite to the slate, a quartzitic slate 
intervening. In the above lists such beds are classified as quartzite. 
The Pond quarry measures about 500 feet along the strike and nearly 100 feet 
across it at the top, and from 250 to 300 feet in depth. The beds strike N. 47° E., 
dip 78°-80° SE., without any indication of turning, and the cleavage strikes N. 45° E., 
dips 90°, thus intersecting the bedding at a very acute angle. The grain strikes 
N. 45°-50° W. and dips 90°. The slate is traversed at intervals by horizontal joints, 
which are more frequent in the quartzite — in places from 1 to 4 feet apart. The 
quartzite also has joints, striking N. 65° W. and dipping 25° N. 65° E., which often ; 
are veined with quartz. There are also vertical diagonal joints striking about north- 
