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CHAPTER II. 
Arrangement of the materials composing the earth's crust — The existing con- 
tinents chiefly composed of subaqueous deposits — Distinction between sedi- 
mentary and volcanic rocks — Between primary, secondary, and tertiary — 
Origin of the primary — Transition formations — Difference between secondary 
and tertiary strata — Discovery of tertiary groups of successive periods — Paris 
basin — London and Hampshire basins — Tertiary strata of Bordeaux, Pied- 
mont, Touraine, &c. — Subapennine beds — English crag — More recent deposits 
of Sicily, &c. 
GENERAL ARRANGEMENT OF THE MATERIALS COMPOSING 
THE EARTH'S CRUST. 
When we examine into the structure of the earth's crust (by 
which we mean the small portion of the exterior of our planet 
accessible to human observation),whether we pursue our investi- 
gations by aid of mining operations, or by observing the sections 
laid open in the sea cliffs, or in the deep ravines of mountainous 
countries, we discover everywhere a series of mineral masses, 
which are not thrown together in a confused heap, but arranged 
with considerable order ; and even where their original position 
has undergone great subsequent disturbance, there still remain 
proofs of the order that once reigned. 
We have already observed, that if we drain a lake, we fre- 
quently find at the bottom a series of recent deposits disposed 
with considerable regularity one above the other ; the upper- 
most, perhaps, may be a stratum of peat, next below a more 
compact variety of the same, still lower a bed of laminated 
shell marl, alternating with peat, and then other beds of 
marl, divided by layers of clay. Now if a second pit be sunk 
through the same continuous lacustrine deposit, at some distance 
from the first, we often meet with nearly the same series of 
beds, yet with slight variations ; some, for example, of the 
layers of sand, clay, or marl may be wanting, one or more of 
