9 
AMERICAN GEOLOGY. 
that there was a plan in the divine mind which has been work¬ 
ing with a special reference to the good of our race; and lastly, 
that the plan of creation, and its scheme of construction, belongs 
to but one system, however far we may go back into the past. 
All our observations respecting the past and present lead to the 
conclusion that the plan of creation is one—that the laws and 
forces which are now in operation have been the same from 
the beginning: therefore, the true method for an interpretation 
of the past, is by those laws and forces which govern the 
present. 
§ 2. Our knowledge of the earth is confined to the earth’s 
crust, by which we mean to include all that part which is 
accessible to human observation. This part is the theatre upon 
which geological events have been acting from remotest periods, 
and still it is safe to draw inferences respecting phenomena 
belonging to the deeper seated parts, provided they are in 
accordance with established principles, or with what we know. 
§ 3. The earth’s crust is composed of rocks, in which term 
geologists include not only consolidated materials, but sands, 
clays, soils, and fluids. Strictly speaking, the earth’s crust is 
composed of rock and water. We might perhaps reckon also 
the free gaseous bodies confined in caverns, which, under favor¬ 
able circumstances, escape into space, as atmospheric air, car¬ 
bonic acid, nitrogen, and ammonia; or they may be regarded 
as things contained in the crust, and as agencies through whose 
force and power the solid crust has changed its phases in time 
and its position in space. Heat should be added to the fore¬ 
going; it operates per se, and gives activity and life to the 
liquids and gases which permeate the crust and fill its empty 
spaces. 
§ 4. The monumental records of the past are of two kinds, 
the physical and the organic. To the former belong the impress 
of the movements of the earth’s crust upon itself, or upon the 
different strata which were deposited in different periods; to 
the latter, the preservations of plants and animals. Their 
remains occur in groups, and represent the forms of the differ- 
