26 J. D. Dana— Geological Relations of the 
The rock that adjoins a belt or stratum of limestone is com- 
monly a mica schist or micaceous gneiss in which black mica 
else hornblende schist; and the beds are not unfrequently pyri- 
tiferous. But the rock may also be ordinary gneiss, or a light- 
colored ésidebadiio gneiss; or it may consist of intercalations of 
these with the more micaceous kinds, and in the northeastern 
This association of the limestone with rocks containing much 
black mica or hornblende is, in fact, association with rocks con- 
taining much tron :—an association whiel exists in similar cases 
throughout the Green Mountain region; and corresponding re- 
gions in the State of Pennsylvania and others farther to the 
southwest ; as is indicated by the rusting tendency of the schists 
in the vicinity of limestone beds, and, still more, by the occur- 
rence of great limonite beds made from the iron of the lime- 
stones and adjoining schists. 
Furthermore, this quality of these metamorphic schists is a 
consequence of the ferruginous character of the original sedi- 
mentary beds underlying or overlying the limestone strata. 
— iron = those sediments went, for the most part, at the 
sometimes, garnet. The distinction between these schistose 
micaceous rocks and a hard thick-bedded feldspathic gneiss is, 
to a large degree, therefore, the equivalent of that in regions o 
sedimentary rocks between highly ferruginous and slightly fer- 
ruginous beds, and ong it is not necessarily of much geo- 
logical importance. This fact, which is abaladanity established 
by the frequent oe gradations im such rocks from extreme 
from the looks or composition alone, that the hard, gray feld- 
- 
Men ase Pee 
