SILLIMAN'S INTRODUCTION. O 



lodged from still earlier beds. In addition to the products of actual 

 volcanoes — the ignigenous rocks, crystallized or deposited from 

 fusion, both in the earliest and in many of the more modern epochs 

 — injected among, and traversing strata of all descriptions and ages, 

 and thus assimilated to known products of internal fire, the proper 

 rocky masses, the granites, sienites, porphyries, serpentines, and 

 traps, give authentic information of the unapproachable gulf of fire 

 whence they were projected. 



The internal waters that gush cool from the fountains on the land 

 or under the sea, or those that spout in boiling geysers from the deep 

 caverns where their imprisoned vapours accumulate explosive force; 

 all these bring to the surface the materials of the interior, and 

 conspire with tornadoes of gas, bursting from volcanoes and other 

 vents, to reveal the deep secrets of the earth. 



5. Its positive tjtiity. — Geology, in addition to its inherent 

 dignity, puts forth strong claims to regard on the ground of positive 

 utility. Every thing reposes upon the mineral kingdom ; it affords 

 to man, directly or indirectly, all the materials of his physical com- 

 fort — all those of national wealth, and all the means of civilization. 

 The most important of physical instruments are derived, imme- 

 diately or remotely, from it, for the vegetable world, equally with 

 the animal, rests upon this basis ; whether we speak of the cedar, 

 the oak, the lichens, or the grasses, all equally derive their support 

 from the elements afforded by the mineral kingdom ; which, in its 

 widest sense, includes not only the solid earth, but its waters, and 

 all its fluids — its atmosphere and all its gases. The vegetable 

 kingdom borrows not a few elements from the mineral world ; 

 oxygen, carbon, hydrogen, and even nitrogen, and all that are indis- 

 pensable to vegetable life, are found in the waters, or in the atmo- 

 sphere ; while other elements or compounds, adapted to particular 

 purposes, are derived from various mineral sources ; the soil, for 

 example, affords silica, which enters into the composition of the 

 epidermis of grasses, bamboos, equiseta, &c. ; and potass and soda, 

 derived from decomposed felspar and other minerals, pass by absorp- 

 tion into the juices of plants. Even animal and vegetable manures 

 form no exception, for their elements have a similar origin, and 

 consist almost entirely of the substances indispensable to vegetable 

 growth. 



Thus, while we explore this orb of gases, fluids, and solid rocks, 

 we shall gain the most interesting knowledge, and much positive 



