Geological Equivalents. | 133 
tions, their repetitions ‘and original absence, often require intrinsic 
characters for determining the places in the system to which they 
should be referred. Werner himself found it necessary to resort to. 
mineral contents in some cases. Hence we have a topaz rock and a 
diallage rock. His successors have given us, on the same principle, 
metalliferous, saliferous and carboniferous rocks. 1 found myself 
compelled to follow these examples, in describing the rocks in the 
state of New York, which embrace a stratum of argillaceous iron ore, — 
more than two hundred miles in length. They seem not to occuron _ 
the eastern continent, excepting in very limited beds. Therefore, 
I ventured, seven years ago, to describe them under the name, Fer- 
riferous rocks; to which I have heard no objections. 
hen rocks of great extent can be inspected in situ, neither. 
mineral constituents nor contents are taken into consideration, as 
principal means for ascertaining their relative positions in a system. 
But by an acquaintance with such decisive cases, we may learn 
characters, to be usefully employed in doubtful cases. Rules found- 
ed on such characters are always to be corrected, however, when 
at variance with the laws of superposition, as shown by strata de- 
cidedly in place, Throughout the western part of the state of 
ew York, and of the state of Pennsylvania, . 
nist extent, and their order of superposition is 
extent, 
le 
their southern sides, near the Helderberg mountains, southwest from 
"Y- Trepresented these terminations in a profile sketch over a 
Map, exhibiting the Economical Geology of the state of New York, 
and part of the adjoining states, published about a year and a half 
vin referred for directions to the following students: Messrs. Edgerton of 
the Ne chards of White creek, (the latter was most successful in finding amber in 
Livin rsctgaoaae lignite,) H. H. Eaton of Lexington, Ken., Storrs of Lebanon, N. H. 
Sinan * of Red Hook, White of Cherry Valley, (the three last, aided by Mr. verieate 
Tows T. Middletown, N.J. were most successful collectors at the marl pits,) Bar- 
re vay n, W. B. Eaton, of Troy, Sager of Bethlehem, Booth and Bol- 
ton of N » Cannon, 
Devo} or Be York, Cobb of Galway, Hill of Worcester, Mass. Noble of Carbondale, : 
haghticoke. 
# 
’ 
=F 
ce 
