200 J. D. Dana— Geological Relations of the 
and even chrysolitic rocks are sometimes near by. The iron 
ore has been found at several points within a mile north and 
northeast of Cruger’s, and also three or four miles distant in 
been made. Thin magnetite beds occur also on Cruger’s Point, 
in the soda-granite and quartz-dioryte, half a mile west of the 
railroad station. The material is fine-grained, nearly black in 
color, chloritic like the preceding, and is usually associated 
with black mica. These beds are the subject of special de- 
scriptions beyond. 
Among the localities in eastern Cortland, three are situated in 
a ridge or mountain running northward from Colabaugh Pond. 
One is at the southern end of the ridge, just north of the pond; 
another, near the road crossing it, about a mile farther north; 
and the third, at the north end of the ridge, nearly three miles 
from the pond, south of “‘Summer Hill.” The magnetite, at 
each of these places, contains some disseminated corundum, 
making it a serviceable emery, and two of these mines have 
been worked for the emery ; much of it also is chloritic. Fib- 
rolite in small needles and divergent tufts is found with the 
ore at each locality. 
B. THE RELATION OF THESE CORTLAND ROCKS TO THE OTHER ROCKS OF WESTCHES- 
TER COUNTY. . 
The above brief description of the Cortland rocks prepares 
the way for a consideration of their relation to the other rocks 
of the county. The following questions arise: Are they one 
with the latter in system? are they rocks of an earlier system? 
or are they eruptive rocks, and not metamorphic, and, hence, 
of no bearing on the general question as to the age of the West- 
chester limestones and the associated schists? If it can be 
shown that the second or last supposition is the true one, the 
subject before us is rid by a stroke of the most serious of its 
perplexities. 
1, Evidences of more or less complete fusion. 
The evidences of fusion or plasticity are many; and, taking 
them collectively, they are decisive. They are exhibited in 
