
CHAPTER We 
STRATIFICATION AND THE FORMATION OF ROCK-BEDS 
Consolidation of Incoherent Accumulations. Lamination and Strati- 
fication. Extent and Termination of Beds. Contemporaneous 
Erosion. Grouping of Strata. Contemporaneity of Strongly Con- 
trasted Strata. Diagonal Lamination and Stratification. Surface- 
markings, 
TECTONIC or Structural Geology treats of the arrangement 
of rocks, or the mode of their occurrence. It deals, in short, 
with the architecture of the earth’s crust. The studyaer 
rocks, Petrography, is concerned simply with the nature and 
origin of rocks as aggregates of mineral matter. For the 
purposes of geology, however, this is not sufficient—rocks must 
be studied not only in hand specimens, but as constituents of 
the earth’s crust. The geologist must take note of the 
positions they occupy as rock-masses, and the relation which 
the various rock-masses bear to one another. It is only by 
such observations that the order of succession, or, in other 
words, the relative age of rock-masses, can be ascertained, 
and the particular conditions under which they were formed, 
and the various changes they have since undergone, can be 
determined. It is, therefore, hardly too much to say that our 
knowledge of the many revolutions which have affected the 
earth’s surface—the ever-changing geographical conditions of 
the past—is largely based on the study of structural geology. 
In discussing the important subject to which the following 
chapters are devoted, attention must be largely confined to a 
description of rock-structures; but it may be helpful to the 
student now and again to consider what such structures 
mean, and to show how they may be interpreted by reference 
to existing operations of nature, 
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