If 



ROCKS. IbV 



LESSON 85. 



Relative Situation of Rocks. 



Pseu'do, a prefix, which, put before words, signifies false, counter- 

 feit. 



Lichen, (pronounced Lik'en) a cryptogamous plant, growing on 

 rocks ; in Ireland, a species of Lichen is prepared and used as 

 food. 



Presented to the cultured eye of taste, 

 No rock is barren, and no wild is waste. 



Rocky masses, variously placed over each other, com- 

 pose the whole crust of the earth, to the greatest depth that 

 the industry of man has been able to penetrate. Now these 

 rocks, with respect to each other, occupy a determinate 

 situation, which holds invariably in every part of the earth. 

 Thus limestone is no where found iinder granite, but always 

 above it. Werner has chosen this relative situation as the 

 basis of his classification of rocks. He divides them into 

 five classes which are called formations ; as primitive, transi- 

 tion, fletz, alluvial, and volcanic. The primitive formations 

 are of course the lowest of all, and the alluvial constitute the 

 very surface of the earth ; for the volcanic, as is obvious, are 

 confined to particular points. Not that the primitive are 

 always at a great depth under the surface, very often they 

 are at the surface and constitute mountains. In such cases 

 the other classes of formations are wanting altogether. Li 

 like manner the transition and other formations may, each ia 

 its turn, occupy the surface, or constitute the mass of a moun- 

 tain. In some cases all the subsequent formations which 

 ought to cover them are wanting in that particular spot. 

 Each of these grand classes of formations consists of a greater 

 or smaller number of rocks, which occupy a determinate 

 position with respect to each other, and which like the great 

 formations may often be wanting in particular places. 



The rocks which constitute the primitive formations are 

 very numerous. They have been divided into several sets, 

 such as granite, gniess, mica-slate, and others. It deserves 

 attention, that the rocks constituting them are all chemical 

 combinations, and generally crystallized ; that they contain 

 no petrifactions ; and that the oldest formations contain no 

 carbonaceous matter. Transition rocks are not so nu- 



