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BOOK IV. 
GEOTECTONIC (STRUCTURAL) GEOLOGY, 
OR THE ARCHITECTURE OF THE EARTH’S CRUST. 
THE nature of minerals and rocks and the operations of the 
different agencies by which they are produced and modified having 
been discussed in the two foregoing books, there remains for con- 
sideration the manner in which these materials have been arranged 
so as to build up the crust of the earth. Since by far the largest 
portion of this crust consists of sedimentary or aqueous rocks, it will ~ 
be of advantage to treat of them first, noting both their original 
characters as resulting from the circumstances under which they 
were formed, and the modifications subsequently effected upon them. 
Many superinduced structures, not peculiar to sedimentary, but 
occurring more or less markedly in all rocks, may be conveniently 
described together. ‘The distinctive characters of the igneous or 
eruptive rocks, as portions of the architecture of the crust, will then 
be described; and lastly, those of the crystalline schists and other 
associated rocks to which the name of metamorphic is usually 
applied. 
Part J.—STRATIFICATION AND ITS ACCOMPANIMENTS. 
The term “stratified,” so often applied as a general designation 
to the aqueous or sedimentary rocks, expresses their leading 
structural feature. Their materials, laid down for the most part on 
the bed of the sea and the floors of lakes and rivers under conditions 
which have been already discussed in Book III., are disposed in 
layers or strata, an arrangement characteristic of them alike in hand- 
specimens and in cliffs and mountains (igs. 182 and 183). Not 
that every morsel of aqueous rock exhibits evidence of stratification. 
But it is this feature which is least frequently absent. The general | 
characters of stratification will be best understood from an explana- 
tion of the terms by which they are expressed. 
Forms of Bedding.—Laminez are the thinnest paper-like 
layers in the planes of deposit of a stratified rock. Such fine layers 
only occur where the material is fine-grained, as in mud or shale, or 
where fine scales of some mineral have been plentifully deposited, as 
in micaceous sandstone. In some laminated rocks the laminae cohere 
so firmly that they can hardly be split open, and the rock will 
