18 PRINCIPLES OF PALAZONTOLOGY. 
posits by its own action. Upon every coast-line the sea is 
constantly eating back into the land and reducing its com- 
ponent rocks to form the shingle and sand which we see upon 
every shore. The materials thus produced are not, however, 
lost, but are ultimately deposited elsewhere in the form of new 
stratified accumulations, in which are buried the remains of 
animals inhabiting the sea at the time. 
Whenever, then, we find anywhere in the interior of the land 
any series of beds having these characters—composed, that is, 
of distinct layers, the particles of which, both large and small, 
show distinct traces of the wearing action of water—whenever 
and wherever we find such rocks, we are justified in assuming 
that they have been deposited by water in the manner above 
mentioned. Either they were laid down in some former lake 
by the combined action of the streams which flowed into it; 
or they were deposited at the mouth of some ancient river, 
forming its delta; or they were laid down at the bottom of the 
ocean. In the first two cases, any fossils which the beds 
might contain would be the remains of fresh-water or terres- 
trial organisms. In the last case, the majority, at any rate, of 
the fossils would be the remains of marine animals. 
The term “ formation” is employed by geologists to express 
“any group of rocks which have some character in common, 
whether of origin, age, or composition” (Lyell); so that we 
may speak of stratified and unstratified formations, aqueous 
or igneous formations, fresh-water or marine formations, and 
so on. 
CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 
The Aqueous Rocks may be divided into two great sections, 
the Mechanically-formed and the Chemically-formed, includ- 
ing under the last head all rocks which owe their origin to 
vital action, as well as those produced by ordinary chemical 
agencies. 
A. MECHANICALLY-FORMED Rocks. — These are all those 
Aqueous Rocks of which we can obtain proofs that their 
particles have been mechanically transported to their present 
situation. Thus, if we examine a piece of conglomerate or 
puddingstone, we find it to be composed of a number of 
rounded pebbles embedded in an enveloping matrix or paste, 
which is usually of a sandy nature, but may be composed ot 
carbonate of lime (when the rock is said to be a “ calcareous 
conglomerate”). The pebbles in all conglomerates are worn 
and rounded by the action of water in motion, and thus show 
