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 

 receive 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 palaeonto- 

 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. 



