PALEONTOLOGICAL BREAKS. 195 



when no unequivocal traces of preexisting life are anywhere to be 

 met with in the formation next preceding. So absolutely universal 

 is this condition that it almost staggers belief. It cannot rationally 

 be conceived that the varied Cambrian fauna could have come into 

 existence de se, without there being a line of progenitors to account 

 for its existence; but, if such progenitors did exist, which was 

 doubtless the case, what has become of their remains ? Can it 

 be that all over the world, as far as we know, every fragment of 

 such a pre-Cambrian fauna should have been so completely wiped 

 out as to leave not a determinable vestige behind ? It must be 

 confessed this seems very incredible, seeing with what absolute 

 perfection many of the oldest, and in many respects the most deli- 

 cate, structures have been preserved through all the vicissitudes of 

 geological time. The hexactinellid sponges of the Cambrian and 

 Silurian periods, the Silurian Foraminifera, and scarcely less so the 

 graptolites, bear ample testimony to a most astonishing power of re- 

 sistance. To account for such a wholesale obliteration, we must in- 

 voke the aid of a kind or degree of metamorphic action very different 

 from that which has since been made known to us, for it can scarcely 

 be supposed that the ordinary action extending back through only 

 one more period of geological time could have produced such pro- 

 found results. And it is not only from a comparatively brief period 

 of time that we must explain the utter absence of organic traces, but 

 from a period which, in the opinion of many geologists, may have 

 been of equal duration with the entire interval that has elapsed since 

 the deposition of the Cambrian sediments. But, even granting this 

 unknowable form of regional metamorphism, it still remains a mys- 

 tery how its effects could have been so universal as to wipe out 

 every vestige of an indisputable pre-Cambrian fauna. It is very 

 possible that the limestone of the Laurentian rocks owes its ex- 

 istence to organic agencies, and therefore represents in part this 

 earlier fauna ; but even admitting this to be so, it helps the mat- 

 ter very little, since the limestone is overlaid by younger crystal- 

 line rocks, which are no less destitute of organic traces than the 

 deposits underlying it. For the same reason the existence or non- 

 existence, as an animal, of the much - debated Eozoon, does not 

 affect the point at issue; on the contrary, the total absence of de- 

 terminable organic traces, either above or below the Eozoon line, 

 would, in itself, apart from all other evidence, constitute strong 



