Stratification Planes. — Keyes. 295 
The phenomenon of bedding, or stratification, belongs to the 
class of original rock structures, in contradistinction to struc- 
tures acquired. It results from transportation and deposition 
of rock particles derived from other disintegrated rocks. In 
the operation of the gradational processes three distinct phases 
are represented, according as the agency is wind, ice, or water. 
Of these, the hydric effects are by far the most important. To 
these are due nearly all the phenomena connected with strat- 
ification structures. 
The truly stratified structure in rocks has for its funda- 
mental proposition the doctrine that all materials that are de- 
rived from the wasting of the land areas of the globe finally 
find their way into the sea, there to be laid down in new forma- 
tions. Deposits formed in lakes and along rivers are also 
often stratified, but their existence is usually only temporary. 
Such sediments are also sooner or later swept into the sea. All 
the sedimentary rock masses, except a few of the more recent, 
are thus considered as of maritime origin. 
When the finer rock materials from the degraded land 
areas are carried into the quiet waters of the sea they are soon 
thrown down roughly according to their size and weight. But 
as the sea floor is constantly rising and sinking, and as the 
shore is continually retreating and advancing, homogeneous 
accumulations of any great extent are not possible. The min- 
ute changes in the conditions of deposition give rise to lamina- 
tion in the strata and to the bedded structures, and the greater 
changes to the alternation of beds. 
Local s^ratigraphic relationship is usually more or less dis- 
guised by rock displacement. Since the stratified character 
of the sedimentary rocks is imparted as the rock mass is 
formed, it is regarded as an original structure, and the layers 
and the stratification planes are presumed to be at first dis- 
posed nearly horizontally. The stratified rocks have thus fur- 
nished our most ready means of determining the succession of 
the events that a given district has passed through. The sub- 
sequent or acquired structures, as flexures and dislocations, 
can also thus be distinguished and measured. In the case of 
the massive crystallines, such phenomena can rarely be deter- 
mined. With the schistose rocks, the various disturbances 
have been repeated so often that, except in a few instances, the 
