312 Hie American Geologist. November, 1894 
microscopic characters with the pyroxene of the pyroxene- 
rock. (3) Graphite scales are found in the quartz-rock as 
well as in the crystalline limestone. 
The pyroxene-rock and quartz-rock appear to result from 
the development, on a large scale, of accessor} 7 minerals which 
are common everywhere in the limestone. The reason for 
their development is not known. It does not appear to be due 
to local metamorphism by eruptive rocks, but is rather a result 
of the general metamorphism which the limestone has under- 
gone. 
Magnetite, as has already been shown, is one of the most 
abundant accessory minerals of the limestone and occurs in 
irregular grains and aggregates. In some places this magne- 
tite increases in proportion to the calcite until it forms the 
whole, or nearly the whole, of the rock, the calcite then being 
wholly absent or occurring in small amounts between the 
grains of magnetite. The rock is then frequently mined as an 
iron-ore. There are all gradations between a pure crystalline 
limestone and a typical limestone iron-ore. The origin of the 
limestone iron-ore is the same as the origin of the accessory 
magnetite which occurs in scattered, irregular grains in the 
white limestone. It seems most probable that both are de- 
rived from iron included in the limestone as an impurity at 
the time of its formation. The magnetite occurs in the lime- 
stone in scattered grains and in masses, and in beds. Where 
it forms beds it differs from its occurrence in isolated grains 
only in its relative abundance, and the beds of limestone iron- 
ore grade into the pure limestone beds above and below. These 
beds may be due to primary deposition as beds, or, as seems 
more probable, to a later segregation of isolated grains into 
planes, either bedding-planes or planes of secondary origin 
due to dynamic action. 
It is not purposed here to enter into a discussion of the 
origin of these accessory minerals of the crystalline limestone. 
The limestones are cut by numerous eruptive rocks, mainly 
diorite and pegmatite, and, in a less degree, diabase. It does 
not seem probable that the accessory minerals are the result 
of local metamorphism by these eruptives, for the minerals 
occur widely and uniformly disseminated throughout the 
limestone and at a distance from the eruptives. Further, they 
