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, including under the last head all rocks which owe their origin to vital action, as well as those produced by ordinary chemical agencies.
[Illustration: Fig.

6 .-- Microscopic section of a calcareous breccia in the Lower Silurian (Coniston Limestone) of Shap Wells, Westmoreland.

The fragments are all of small size, and consist of angular pieces of transparent quartz, volcanic ashes, and limestone embedded in a matrix of crystalline limestone.

(Original.)] 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 of carbonate of lime (when the rock is said to be a "calcareous conglomerate").