4 MINERALOGY AND LITHOLOGY. 



composition, mode of origin, and instructive peculiarities of our rocks 

 and minerals. 



A rock is a mineral aggregate. It is a mass that is composed either of 

 one mineral, or of a mixture of several. Hence, in studying the materials 

 of the earth's crust, we must begin with mineralogy ; and when we are 

 familiar with the simple minerals, we can then study their aggregations, 

 which form simple or complex rocks. In this work, therefore, the min- 

 erals that have been found in the state will first be enumerated, and their 

 noticeable peculiarities will be pointed out. The second part will be 

 devoted to a description of the rocks. 



Minerals are often attractive and beautiful as specimens. Natural 

 crystals and gems are admired by all. Rocks are generally admired as 

 forming masses ; but rocks are also beautiful when we study them with 

 searching care, — when their minutest structure is brought into view by 

 the aid of the microscope. Moreover, most instructive results are obtained 

 by this method of study. Other portions of this geological report have 

 treated of the age of our minerals and rocks, of their distribution and 

 relations to one another, and of the structure of the country which results 

 from the method of their arrangement. In this part, the results of labo- 

 ratory work are given ; and the methods of physical and chemical miner- 

 alogy are introduced as a supplement to the work in the field. Micro- 

 scopic work has been made prominent, since by this method of study 

 such weighty results have been obtained by foreign laborers, that is has 

 now become indispensable in the prosecution of geological work. The 

 author's aim has been to apply the newer methods of study to our old 

 rocks; to try to show the value of those methods, and how many inter- 

 esting things can be observed with their aid. He hopes that the many 

 observations new to our section of country, and the variations here fur- 

 nished on the observations made elsewhere, will be considered of value. 

 He wishes to apologize for the incompleteness of the work, and the injus- 

 tice done a grand series of rocks. Where the labors of a lifetime could 

 not exhaust the observations that might be made, the work of a very 

 short time, on limited material, can do but little more than draw the 

 attention of students to this field of study. 



The author docs not wish to enter on this work without paying his 

 tribute to the German lithologists who have developed the methods that 



