THE FOSSILIFEROUS ROCKS. 19 



\Yhenever, 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 organ- 

 isms. 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 em- 

 bedded 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 "Calcareous conglomerate"). The peb- 

 bles in all conglomerates are worn and rounded by the action of 

 water in motion, and thus show that they have been subjected 

 to much mechanical attrition whilst they have been mechanically 

 transported for a greater or less distance from the rock of 

 which they originally formed part. The analogue of the old con- 

 glomerates at the present day is to be found in the great beds 



