4 | -- GEOLOGY. 
of a few yards, the evidence of a most varied and complicated series 
of changes in physical geography, as well as an abundant and inter- ~ 
esting suite of organic remains. These and other characteristics of 
the geological record will become more apparent and intelligible to 
the student as he proceeds in the study of the science. 
In the present volume the subject will be distributed under the 
following leading divisions. , 
1. The Cosmical Aspects of Geology.—tIt is desirable to realise — 
some of the more important relations of the earth to the other — 
members of the solar system, of which it forms a part, seeing that — 
seological phenomena are largely the result of these relations. 
The form and motions of the planet should be briefly touched 
upon, and attention should be directed to the way in which these | 
planetary movements influence geological change. The light cast — 
upon the early history of the earth by researches into the composition 
of the sun and stars deserves notice here. - 
2. Geognosy,—an Inquiry into the Materials of the Harth’s 
Substance.—This division describes the constituent parts of the earth, 
its envelopes of air and water, its solid crust, and the probable con- — 
dition of its interior. Especially, it directs attention to the more im- — 
portant minerals of the crust, and the chief rocks of which that crust is — 
built up. In this way it lays a foundation of knowledge regarding ~ 
the nature of the materials constituting the mass of the globe, from — 
which we may next proceed to investigate the processes by which 
these materials are produced and altered. 
3. Dynamical Geology embraces an investigation of the operations — 
which lead to the formation, alteration, and disturbance of rocks. — 
It considers the nature and operation of the processes that have — 
determined the distribution of sea and land, and have moulded the — 
forms of the terrestrial ridges and depressions. It further investi- 
gates the changes which are in progress over the surface of the land, 
whether these are due to subterranean disturbance, or to the effect 
of operations above ground. Such an inquiry necessitates a careful 
study of the existing geological economy of nature, and forms a 
fitting introduction to the investigation of the geological changes of - 
former periods, ‘This and the previous section, including most of — 
what is embraced under Physical Geography and Petrogeny or 
Geogeny, will here be discussed more in detail than is usual in ~ 
geological treatises. - 
4. Geotectonic, or Structural Greology—the Architecture of the Earth. 
—This section of the investigation discusses the mode of arrange=_ 
ment of the various materials composing the crust of the earth. It 
proves that some have been formed in beds or strata, whether by 
the deposit of sediment on the floor of the sea, or by the slow aggre- 
gation of organic forms, that others have been poured out from 
subterranean sources in sheets of molten rock, or in showers of loose 
dust, which have been built up into mountains and plateaux. It 
further shows that rocks originally laid down in almost horizontal 

