52 PRINCIPLES OF PALZONTOLOGY. 
has not been continuity in any given area, still the geological 
chain could never have been snapped at one point, and taken 
up again at a totally different one. Thus we arrive at the 
conviction that continuity is the fundamental law of geology, 
as it is of the other sciences, and that the lines of demarca- 
tion between the great formations are but gaps in our own 
knowledge. 
CHARTER: Y. 
CONCLUSIONS TO BE DRAWN FROM FOSSILS. 
We have already seen that geologists have been led by the 
study of fossils to the all-important generalisation that the vast 
series of the Fossiliferous or Sedimentary Rocks may be 
divided into a number of definite groups or “ formations,” 
each of which is characterised by its organic remains. It may 
simply be repeated here that these formations are not properly 
and strictly characterised by the occurrence in them of any 
one particular fossil. It may be that a formation contains 
some particular fossil or fossils not occurring out of that 
formation, and that in this way an observer may identify a 
given group with tolerable certainty. It very often happens, 
indeed, that some particular stratum, or sub-group of a series, 
contains peculiar fossils, by which its existence may be deter- 
mined in various localities. As before remarked, however, the 
great formations are characterised properly by the association 
of certain fossils, by the predominance of certain families or 
orders, or by an assembdage of fossil remains representing the 
“life” of the period in which the formation was deposited. 
Fossils, then, enable us to determine the age of the deposits 
in which they occur. Fossils further enable us to come to 
very important conclusions as to the mode in which the fossil- 
iferous bed was deposited, and thus as to the condition of the 
particular district or region occupied by the fossiliferous bed 
at the time of the formation of the latter. If, in the first 
place, the bed contain the remains of animals such as now 
inhabit rivers, we know that it is “ fluviatile”’ in its origin, and 
that it must at one time have either formed an actual river- 
bed, or been deposited by the overflowing of an ancient 
stream. Secondly, if the bed contain the remains of shell- 
fish, minute crustaceans, or fish, such as now inhabit lakes, 
