TRANSITION AND SECONDARY STRATA. 
89 
ing beings wliich hav'e been destroyed, it is much more proba¬ 
ble that tbej’ assumed their present lorm before there was either 
a plant or an animal to be imbedded in them. 
4S. Prop. III. 'I'/te transilian and secondary 7'ocks tvhich 
are 77010 Jon 7 id with their strata highly hiclhied, were deposit¬ 
ed a7)d co7isolidated i7i horizontal beds. 
9'hey bear an intimate resemblance to those accumulations of 
fine clay, sand, and gravel, that are now found in the bottoms ot 
lakes and the estuaries of rivers. 'I'here are the same alternations 
of coarse and tine materials, indefinitely repeated, and with¬ 
out any approach to regularity. They are evidently made up 
of what was once a loose mass, destitute of cohesion, and which 
by the infiltration of siliceous, calcareous, or ferruginous matter 
and by other causes has been converted into rocks. Such a mass 
if placed upon a ])lane that is consideralily inclined, will not ar¬ 
range itself in beds or layers parallel to the surlace of the plane, 
but will roll, sink, or slide dou 11 to its lowest point. In so doing 
it will only obey the most general ol all the laws that regulate 
the material world, the law of gravity. 
The case is particularly clear when very thin la)^ers of shells 
or pebbles are interposed between two adjacent strata. It would 
in many instances, have been quite impossible for them to gain 
the ])ositions in which they are found, in any other way, than by 
being strewed uniformly over an horizontal surface, and then 
covered with a stratum of a different kind. U hese arguments 
will not apply to all the transition and secondary strata : they 
are applicable to the most of them ; and the rest will be found so 
alternating with, or imbedded in those to which it does apply, that 
whatever decision we pass upon the one class, we shall find our¬ 
selves under the necessity of extending to the other. 
49. Prop. IV. The secondary, tra7isition, and in many 
cases the pri77iitii'e strata, have bee7i shijted from their origi¬ 
nal positions i7ito those ivhich they 7iow occupy, by forces ivhich 
have operated si7ice then' consolidatio7i. 
This proposition follows as a necessary corollary from the two 
preceding, and is introduced less with a view to a formal proof 
of its truth, than to an enquiry respecting the nature and mode 
of action of the forces by which the changes referred to in it have 
been produced. If these strata were deposited and consolidated 
in horizontal beds, and are now found sometimes almost in a ver¬ 
tical position, it is plain that a force of some kind has been ap¬ 
plied to them by which their situation has been changed. It 
may have been the force of gravity, the substance which support¬ 
ed one of their edges having been removed, and that edge left to 
subside by its own weight; or the other edge may have been 
lifted up by a force acting from beneath. 
A mill-pond which has been covered with a thick sheet of ice 
during a cold night, and from which a part of the water has been 
drained off, the next day, furnishes a good representation of the 
