d this we can best
do by considering the laws under which strata of a similar nature are now
being deposited as sedimentary beds.

A great proportion consists of sandstone. Now sandstone is the result of
sand which has been deposited in large quantities, having become
indurated or hardened by various processes brought to bear upon it. It is
necessary, therefore, first to ascertain whence came the sand, and
whether there are any peculiarities in its method of deposition which
will explain its stratification. It will be noticed at once that it bears
a considerable amount of evidence of what is called "current-bedding,"
that is to say, that the strata, instead of being regularly deposited,
exhibit series of wedge-shaped masses, which are constantly thinning out.

Sand and quartz are of the same chemical composition, and in all
probability the sand of which every sandstone in existence is composed,
appeared on this earth in its first solid form in the shape of quartz.
Now quartz is a comparatively heavy mineral, so also, therefore, will
sand be. It is also very hard, and in these two respects it differs
entirely from another product of sedimentary deposition, namely, mud or
clay, with which we shall have presently to deal when coming to the
shales. Since quartz is a hard mineral it necessarily follows that it
will suffer, without being greatly affected, a far greater amount of
wearing and knocking about when being transported by the agency of
currents and rivers, than will a softer substance, such as clay. An equal
amount of this wearing action upon clay will reduce it to a fine
impalpable silt. The grains of sand, however, will still remain of an
appreciable average size, and where both sand and clay are being
transported to the sea in one and the same stream, the clay will be
transported to long distances, whilst the sand, being heavier, bulk for
bulk, and also consisting of grains larger in size than grains of clay,
will be rapidly deposited, and form beds of sand. Of course, if the
current be a violent one, the sand is transported, not by being held in
suspension, but rather by being pushed along the bed of the river; such
an action will then tend to cause the sand to become powdered into still
finer sand.

When a river enters the sea it soon loses its individuality; it becomes
merged in the body of the ocean, where it loses its current, and where
therefore it has no power to keep in suspension the sediment which it h