PRELIMINARY REMARKS. 
39 
therefore prefer the adoption of the term lamination to be 
applied to the rocks designated, rather than to continue and 
extend the use of the term stratification. I would restrict this 
to sediments, or transported matter, which have been subjected 
to the action of water. 
§ 34. We may observe frequently a condition in massive and 
stratified rocks which is not due to the conditions which existed 
at the time of their formation. In granite, for instance, where 
it is exposed to disintegrating agencies, there may be observed 
a separation of its mass into laminse, or into thick tabular 
masses, simulating a laminated rock. When this condition is 
examined it may be referred.to a molecular force, or to a con¬ 
cretionary movement of its particles. The separation takes 
place in parallel planes, but they are usually curvilinear. 
Sedimentary* rocks undergo changes from the operation of the 
same forces; the original planes of stratification are obliterated 
and the new planes which are formed are concentric, and 
arranged around a nucleus. Another change takes place in 
rocks whose particles are bathed in water. Clays, and clay 
slates, and limestones of all ages, contain rounded masses which 
are known as septaria, clay stones, or concretions, nodules, &c. 
This is a most interesting change. These bodies may be either 
purely siliceous, or they may be calcareo-aluminous. The sili¬ 
ceous concretions are abundant in the carboniferous limestones 
of Missouri near St. Louis: the flint nodules and layers in 
chalk is another example of the kind. The slates furnish the 
calcareo-aluminous bodies, which in clays are known as clay- 
stones. They are abundant in most clay beds or marls of all 
ages; and those of the slates which are known as septaria, 
differing from the former by their septs, are formed of crystal¬ 
line limestone, barytes or strontian. We are obliged in all 
these instances to recognize a force, by virtue of which the 
molecules are really transferred to central points, where, by 
constant accumulation, they form a nodule, or septaria, or con¬ 
cretion. This force is operative at all times, and upon all 
rocks. Molecules are never at rest until they have acquired a 
