BREAKS IN THE COUESE OF TERRESTRIAL LIFE. 343 



ihat at two places there occur wide gaps in the series 

 whence it is inferred that, on at least two occasions, the 

 previously existing inhabitants of the Earth were almost 

 wholly destroyed, and a different class of inhabitants cre- 

 ated. Comparing the general life on -the Earth to a thread, 

 Hugh Miller says : — 



'' It is contiiiuous from the present time up to the commence- 

 ment of the Tertiary period; and then so abrupt a break occurs, 

 that, with the exception of the microscopic diatomaceaa to which 

 I last evening referred, and of one shell and one coral, not a sin- 

 gle species crossed the gap. On its further or remoter side, how- 

 ever, where the Secondary division closes, the intermingling of 

 species again begins, and runs on till the commencement of this 

 great Secondary division; and then, just where the Palseozoic di- 

 vision closes, we find another abrupt break, crossed, if crossed at 

 all, — for there still exists some doubt on the subject, — by but two 

 species of plant." 



These breaks are considered to imply actual new crea- 

 tions on the surface of our planet ; not only by Hugh Mil- 

 ler, but by the majority of geologists. And the terms 

 Palaeozoic, Mesozoic, and Cainozoic, are used to indicate 

 these three successive systems of life. It is true that some 

 accept this belief with caution : knowing how geologic 

 research has been all along tending to fill up what were 

 once thought wide breaks. Sir Charles Lyell points out 

 that " the hiatus which exists in Great Britain between the 

 fossils of the Lias and those of the Magnesian Limestone, 

 is supplied in Germany by the rich fauna and flora of the 

 Muschelkalk, Keuper, and Bunter Sandstein, which we 

 know to be of a date precisely intermediate." Again he 

 remarks that " until lately the fossils of the coal-measures 

 were separated from those of the antecedent Silurian group 

 by a very abrupt and decided line of demarcation ; but 

 recent discoveries have brought to light in Devonshire, 

 Belgium, the Eifel, and Westphaha, the remains of a fauna 



