12 INTRODUCTION. 



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 terrestrial 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 



o 



so on. 



CHIEF DIVISIONS OF THE AQUEOUS BOCKS. 



The Aqueous Eocks 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 EOCKS. These are all those 

 Aqueous Eocks of which we can obtain proofs that their 

 particles have been mechanically transported to their present 

 site. Thus, if we examine a piece of conglomerate or pud- 

 ding-stone, we find it to be composed of a number of rounded 

 pebbles embedded in an enveloping paste or matrix. The 

 pebbles are worn and rounded, and thus show that they have 

 been subjected to much mechanical attrition, whilst they 



