BREAKS IN THE GEOLOGICAL RECORD. 45 
in different regions are ‘contemporaneous,’ we simply mean 
that they were formed during the same geological period, and 
perhaps at different stages of that period, and we do not mean to 
imply that they were formed at precisely the same instant of time. 
A moment’s consideration will show us that it is only in the 
former sense that we can properly speak of strata being “‘ con- 
temporaneous ;” and that, in point of fact, beds containing 
the same fossils, if occurring in widely distant areas, can hardly 
be “contemporaneous” in any literal sense ; but that the very 
identity of their fossils is proof that they were deposited one 
after the other. If we find strata containing identical fossils 
within the limits of a single geographical region—say in Europe 
—then there is a reasonable probability that these beds are 
strictly contemporaneous, in the sense that they were deposited 
at the same time. There is a reasonable probability of this, 
because there is no improbability involved in the idea of an 
ocean occupying the whole area of Europe, and peopled 
throughout by many of the same species of marine animals. At 
the present day, for example, many identical species of animals 
are found living on the western coasts of Britain and the 
eastern coasts of North America, and beds now in course of 
deposition off the shores of Ireland and the seaboard of the 
state of New York would necessarily contain many of the 
same fossils. Such beds would be both literally and geologi- 
cally contemporaneous; but the case is different if the distance 
between the areas where the strata occur be greatly increased. 
We find, for example, beds containing identical fossils (the 
Quebec or Skiddaw beds) in Sweden, in the north of England, 
in Canada, and in Australia. Now, if all these beds were con- 
temporaneous, in the literal sense of the term, we should have 
to suppose that the ocean at one time extended uninterrup- 
tedly between all these points, and was peopled throughout 
the vast area thus indicated by many of the same animals. 
Nothing, however, that we see at the present day would justify 
us in imagining an ocean of such enormous extent, and at the 
same time so uniform in its depth, temperature, and other 
conditions of marine life, as to allow the same animals to 
flourish in it from end to end; and the example chosen is 
only one of a long and ever-recurring series. It is therefore 
much more reasonable to explain this, and all similar cases, as 
owing to the migration of the fauna, in whole or in part, from 
one marine area to another. ‘Thus, we may suppose an ocean 
to cover what is now the European area, and to be peopled by 
certain species of animals. Beds of sediment—clay, sands, 
and limestones—will be deposited over the sea-bottom, and 
