10 INTRODUCTION. 



Geology treats of the earth in this grand relation. It is as much removed 

 from Mineralogy as from Botany and Zoology. It uses all these depart- 

 ments; for the species under them are the objects which make up the 

 earth and eater into geological history. The science of minerals is more 

 immediately important to the geologist, because aggregations of minerals 

 constitute rocks, or the plastic material in which the records of the past 

 were made. 



The earth, regarded as such an individuality in a world kingdom, has not 

 only its comprehensive system of growth, in which strata have been added 

 to strata, continents and seas defined, mountains reared, and valleys, rivers, 

 and plains formed, all in orderly plan, but also a system of currents in its 

 oceans and atmosphere, — the earth's circulating-system ; its equally world- 

 wide system in the distribution of heat, light, moisture, and magnetism, and 

 of plants and animals; its system of secular variations (daily, annual, etc.) 

 in its climate and all meteorological phenomena. In these characteristics 

 the sphere before us is an individual, as much as a dog, or a tree ; and, to 

 arrive at any correct views on these subjects, the world must be regarded in 

 this capacity. The distribution of man and nations, and of all productions 

 that pertain to man's welfare, comes in under the same grand relation ; for, 

 in helping to carry forward man's progress as a race, the sphere is working 

 out its final purpose. There are, therefore, 



Three departments of science, arising out of this individual capacity of 

 the earth. 



I. GrEOLOGY, wliich treats of (1) the earth's structure, and (2) its system 

 of development, — the latter including its progress in rocks, lands, seas, 

 mountains, etc. ; its progress in all physical conditions, as heat, moisture, 

 etc. ; its progress in life, or its vegetable and animal tribes. 



II. Physiography, which begins where Geology ends, — that is, with 

 the adult or finished earth, — and treats (1) of the earth's final surface- 

 arrangements (as to its features, climates, magnetism, life, etc.); and (2) of 

 its system of physical movements or changes (as atmospheric and oceanic 

 currents, and other secular variations in heat, moisture, magnetism, etc.). 



III. The earth with reference to man (including ordinary Geog- 

 raphy): (1) the distribution of races or nations, and of all productions or 

 conditions bearing on the welfare of man or nations ; and (2) the progressive 

 changes of races and nations. 



The first of these departments considers the structure and growth of the 

 earth ; the second, its features and world-wide activities in its finished state ; 

 the third, the fulfillment of its purpose in man. 



Relation of the earth to the universe. — While recognizing the earth as 

 a sphere in a world kingdom, it is also important to observe that it holds 

 a very subordinate position in the system of the heavens. It is one of the 

 smaller satellites of the sun, — its size about y 2-owoTr ^^^^ ^^ ^^® ^^^- -^^^ 

 the planetary system to which it belongs, although 3,000,000,000 of miles 

 in radius, is but one among myriads, the nearest star being 7000 times 



