33 



crystaline structure; the most recent is fine or com- 

 pact in its texture, and destitute of every appearance 

 of crystalization. A bed of the most ancient limestone 

 is found in Bolton, Massachusetts. In the western part 

 of New York, deposits of the same rock arc constantly 

 forming at the present time. 



ELEMENTS OF ROCKS. 



Notwithstanding the rich and endless variety in the 

 external appearance of rocks, their elements are few 

 and simple; and this apparent and beautiful variety is 

 owing more to the proportion and arrangement of the 

 ingredients which compose them, than to their number 

 or variety. 



Nine simple minerals have been supposed, by many 

 geologists, to be the elementary substances of which 

 all rocks are composed. And it is well known, that 

 four or five of these, constitute by far the greatest part 

 of rocky and mountain masses, and that more than half 

 both of rocks and soils, are formed from two of them. 



The names of these simple minerals, sometimes called 

 the geological alphabet, are quartz, felspar, mica, horn- 

 blende, lime, argillite, (common slate,) gypsum, talc, 

 and chlorite. The two first are the most common and 

 most abundant materials which compose the solid mass 

 of our earth. Of the highest and most extensive moun- 

 tains upon our globe, they are the principal, and to some 

 extent, the only ingredients. They are also, the essen- 

 tial elements of soils, and upon the proper mixture of 

 quartz and felspar, or of silex and alumine, (sand and 

 clay,) the ultimate principles found in these two mine- 

 rals, the fertility of soils depends. 



These two abundant and important minerals in many 

 instances, very nearly resemble each other, tfiough a 

 little experience will enable any one to distinguish them. 

 Quartz is harder than felspar, and much more various in 

 its appearance. It is of every shade of color from 

 nearly black to milk white. The white pebbles so 

 common in the streets and by tUft; way-side, frequently 

 known by the name of flint-stone>, ate a common species 

 of quartz. Gun-flint is another. Sometimes it is 



