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, sahferous 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 occur on 

 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. 



When 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 

 New York, and of the state of Pennsylvania, the rock strata are of 

 vast extent, and their ordef of superposition is open to inspection. 

 There no intrinsic characters are required for ascertaining their po- 

 sitions, in relation to each other, if nothing more is sought. Still 

 there is great difficulty in making out their relative situation, when 

 compared with European strata. It appears probable, that on and 

 near the line of the Erie Canal, there are several rock strata of great 

 extent, (some of them between two and three hundred miles in 

 length,) which have basseting terminations on their northern sides, 

 near the Lakes Erie and Ontario, and cuneiform terminations on 

 their southern sides, near the Helderberg mountains, southwest from 

 Albany. I represented diese 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 



to exist, are referred for directions to the following students : Messrs. Edgerton of 

 Utica, Richards of White creek, (the latter was most successful in finding amber in 

 the New Jersey lignite,) K. H. Eaton of Lexington, Ken., Storrs of Lebanon, N. H. 

 Livingston of Red Hook, Wliite of Cherry Valley, (the three last, aided by Mr. Garret 

 Schank of Middletown, N. J. were most successful collectors at the marl pits,) Bar- 

 rows, Tattle, Cannon, W. B. Eaton, of Troy, Sager of Bethlehem, Booth and Bol- 

 ton of New York, Cobb of Galway, Hill of V/orcester, Mass. Noble of Carbondale, 

 Devol of Schaghticoke. 



