* THE WONDERS OF GEOLOGY. 



pounds to enter into new arrangements, and with the laws which 

 govern these changes. The mechanical laws must also be kept in 

 view ; the weight, pressure, and moving power of solids and fluids, 

 the varieties and force of attraction ; in a word, the dynamics of 

 our globe. Nor can the subject be considered entirely apart 

 from the planetary relations of the earth, as a member of the 

 solar system, and of the innumerable systems which compose the 

 stellular universe. 



Those subtle agents unknown in their essence, but most manifest 

 and potent in their effects — namely, heat, light, electricity, and 

 magnetism, either distinct, or combined in various modifications, 

 demand also a faithful study, that we may comprehend their mani- 

 fold and unceasing effects in the economy of the earth ; nor must 

 the enveloping ocean of aerial fluid, the atmosphere, in which their 

 energy is so largely displayed, be forgotten ; both in its physical 

 and chemical characters, it demands earnest attention. We must 

 also know the outlines of natural history, especially of the mineral 

 species, or, at least, of those which are, or have been, chiefly con- 

 cerned in producing, by their extension or aggregation, the moun- 

 tains and continents, and the entire crust of our planet, so far as it 

 is cognizable by man. Some competent knowledge of mineralogy 

 ought, therefore, to precede the study of geology ; it is true, we 

 may begin with a comparatively small number of the most impor- 

 tant minerals, as our increasing acquaintance with rocks will con- 

 stantly augment our familiarity with the minerals which compose 

 them. 



In like manner, as mineralogy is indispensable to the study of 

 geology, so the other departments of natural history are auxiliary 

 to it in a most important degree. Animals and plants, either entire 

 or dismembered, or in fragments, are contained in almost all kinds 

 of rocks, except the primary and the volcanic ; nor can we assign 

 the limit of organic matter even in these, for we know not how far 

 lire, by softening or fusion, may have obliterated the organic remains 

 that might once have been blended with materials now exhibiting 

 no vestiges of plants or animals. Although we may not be able to 

 mark the precise boundary beyond which organic beings do not 

 appear, it is certain that in all geological epochs, subsequent, 

 at least, to that of the primary rocks, animals and plants have 

 existed in successive families; they have been created, have lived 

 their destined periods, and by the operation of physical causes have 



