PREFACE. 



it would lead to a more thorough knowledge of their characters and relations. 

 These rocks have been termed by some of our ablest geologists, mctnmorpldc. 

 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 diller 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 entided 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 porphyry ; 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 gi-oup into two or more groups. 



