PREFACE. 
5 
it would lead to a more thorough knowledge of their characters and relations. 
These rocks have been termed by some of our ablest geologists, metamorphic. 
If I have interpreted this word rightly, I fully believe that they are by no means 
entitled to this appellation. It will be observed, that in my account of this system, 
I have labored to prove that they are not the Loraine shales, or in other words, 
the Hudson-river group, altered by igneous action. Neither are they the parts 
of the Primary system, as usually located. They may be primary rocks in its 
true sense, and yet differ from those always placed there, as gneiss, hornblende, 
mica and talcose slates. Whatever may be the final opinion in relation to these 
rocks, I have no wish to be supported in the views which I have taken of them, 
unless they are entitled to support. The position the rocks occupy, and the chan¬ 
ges to which they have been subjected, are circumstances which have cast in our 
path many perplexities and obscurities, such as ought to shield any geologist from 
censure, though he may fall into some sad mistakes. On these grounds I hope 
to find refuge, if my well-meant labors have either led me into erroneous doc¬ 
trines, or into an abortive attempt to establish that which has no substantial foun¬ 
dation. 
The Second District, in consequence of its primary character, has led me to 
institute a full examination of those metallic bodies which are found in such large 
masses in this system. I have sought to bring out their true relations to the rocks 
which enclose them. In relation to the magnetic oxide of iron, I now believe 
that I am warranted in supporting the doctrine that it is found under two quite 
distinct conditions : in one case a rock, a primary mass like granite and primary 
limestone; and in another, that of a vein. In this respect it bears an analogy 
with limestone, granite or poi’phyry ; it may be spread out as a rock, or it may 
be injected like trap dykes and other mineral substances of igneous origin. 
In examining the beds or veins of the specular oxide of iron, I have discovered 
some interesting facts, as they appeared to me; particularly in its association 
with serpentine and primary limestone. These facts I was anxious to state fully, 
as they have an important bearing in a practical point of view. The subject, 
from its importance and interest, requires still farther elucidation. 
The sedimentary rocks belong wholly to the lowest position or divisions. Ac¬ 
cording to my observations, they belong to one group ; they are strictly of one 
era or period, as will be seen from the fossils. While I approve of the division 
of the group into elementary rocks, I see no object which can be gained by a 
subdivision of the group into two or more groups. 
