BREAKS IN THE GEOLOGICAL RECORD. 49 
beds of the older series (fig. 18); and a moment’s considera- 
tion will show us what this indicates. It indicates, beyond 
Fig. 18.—Section showing strata of Tertiary age (a) resting upon a worn and eroded 
surface of White Chalk (4), the stratification of which is marked by lines of flint. 
the possibility of misconception, that there was an interval 
between the deposition of the older series and that of the 
newer series of strata ; and that during this interval the older 
beds were raised above the sea-level, so as to form dry land, 
and were subsequently depressed again beneath the waters, to 
receive upon their worn and wasted upper surface the sedi- 
ments of the later group. During the interval thus indicated, 
the deposition of rock must of necessity have been proceeding 
more or less actively in other areas. Every unconformity, 
therefore, indicates that at the spot where it occurs, a more or 
less extensive series of beds must be actually mzssimg ; and 
though we may sometimes be able to point to these missing 
strata in other areas, there yet remains a number of unconfor- 
mities for which we cannot at present supply the deficiency 
even in a partial manner. 
It follows from the above that the series of stratified deposits 
is to a greater or less extent irremediably imperfect ; and in 
this imperfection we have one great cause why we can never 
obtain a perfect series of all the animals and plants that have 
lived upon the globe. Wherever one of these great physical 
gaps occurs, we find, as we might expect, a corresponding ° 
break in the series of life-forms. In other words, whenever we 
find two formations to be unconformable, we shall always find 
at the same time that there is a great difference in their fossils, 
and that many of the fossils of the older formation do not sur- 
vive into the newer, whilst many of those in the newer are not 
known to occur in the older. ‘The cause of this is, obviously, 
D 
