Negative Evidence in Geology. 23 



and marsupial type of mammals. That in an age of Enalio- 

 saurians, most of them carnivorous, the Cetacea may have 

 been superseded to a great extent by large marine reptiles, 

 or may have been much less fully represented than in our 

 own era, when salt-water reptiles are almost unknown, even 

 in the tropics, is highly probable ; just as wingless birds ap- 

 pear for ages to have predominated in New Zealand at the 

 expense of the mammalia ; while marsupial quadrupeds en- 

 joyed a monopoly of Australia to the exclusion of the placental. 

 Yet before we indulge even in this hypothesis, it will be 

 prudent to wait for some years to see whether the reputed 

 relic of a cetacean in the Woodwardian Museum is the only 

 fossil of this class laying claims to so high an antiquity. 



At the risk of appearing to repeat the caution already 

 enjoined by me on the palaeontologist, I will venture to throw 

 out another parting hint on the subject of negative evidence. 

 If we infer the poverty of the flora or fauna of any given 

 period of the past, from the small number of fossils occurring 

 in ancient rocks, we are bound to remember that it has been 

 evidently no part of the plan of Nature to hand down to us 

 a complete or systematic record of the former history of the 

 animate world. We may have failed to discover a single 

 shell, marine or freshwater, or one coral or bone in certain 

 sandstones, such as that of the valley of the Connecticut, 

 where the foot-prints of animals abound. But such failure 

 may have arisen, not because the population of the land or sea 

 was scanty at that era, but because in general the preserva- 

 tion of any relics of the animals or plants of former times is 

 the exception to a general rule. Time so enormous as that 

 contemplated by the geologist may multiply exceptional cases 

 till they seem to constitute the rule, and so impose on the 

 imagination as to lead us to infer the non-existence of crea- 

 tures of which no monuments happen to remain. Professor 

 Edward Forbes in his lectures on Palaeontology has remarked 

 that few geologists are aware how large a proportion of all 

 known species of fossils are founded on single specimens, 

 while a still greater number are founded on a few individuals 

 discovered in one spot. This holds true, not only in regard 

 to animals and plants inhabiting the land, the lake, and the 



