BREAKS IN THE GEOLOGICAL RECORD. 47 
should thus be broadly distinguished. by their life-forms, and 
why they should not rather possess at any rate a majority of 
identical fossils. It was originally supposed that this could be 
explained by the hypothesis that the close of each formation 
was accompanied by a general destruction of all the living 
beings of the period, and that the commencement of each 
new formation was signalised by the creation of a number of 
brand-new organisms, destined to figure as the characteristic 
fossils of the same. This theory, however, ignores the fact 
that each formation—as to which we have any sufficient 
evidence—contains a few, at least, of the life-forms which 
existed in the preceding period; and it invokes forces and 
processes of which we know nothing, and for the supposed 
action of which we cannot account. The problem is an un- 
deniably difficult one, and it will not be possible here to give 
more than a mere outline of the modern views upon the sub- 
ject. Without entering into the at present inscrutable question 
as to the manner in which new life-forms are introduced upon 
the earth, it may be stated that almost all modern geologists 
hold that the living beings of any given formation are in the 
main modified forms of others which have preceded them. it 
is not believed that any general or universal destruction of 
life took place at the termination of each geological period, or 
that a general introduction of new forms took place at the 
commencement of a new period. It is, on the contrary, 
believed that the animals and plants of any given period are 
for the most part (or exclusively) the lineal but modified 
descendants of the animals and plants of the immediately pre- 
ceding period, and that some of them, at any rate, are con- 
tinued into the next succeeding period, either unchanged, or 
so far altered as to appear as new species. To discuss these 
views in detail would lead us altogether too far, but there is 
one very obvious consideration which may advantageously 
recelve some attention. It is obvious, namely, that the great 
discordance which is found to subsist between the animal 
life of any given formation and that of the next succeeding 
formation, and which no one denies, would be a fatal blow to 
the views just alluded to, unless admitting of some satisfactory 
explanation. Nor is this discordance one purely of life-forms, 
for there is often a physical break in the successions of strata 
as well. Let us therefore briefly consider how far these 
interruptions and breaks in the geological and _ palonto- 
logical record can be accounted for, and still allow us to 
believe in some theory of continuity as opposed to the doc- 
trine of intermittent and occasional action. 
