46 LECTURES 



todonic proportions; legions of them were of moderate 

 and diminutive sizes; and their forms must have been 

 almost of endless variety. Think for a moment, as an 

 illustration of my meaning, of the innumerable herds of 

 buffaloes that once covered our Western prairies; and 

 what, do you suppose, would be the chance of discover- 

 ing a fossil specimen of that animal a few thousand 

 years hence? Barely any whatever. Wallace tells us: 



"Fossil remains of land animals are, of course, rarely 

 found except in lacustrine or estuarine deposits; and 

 these are often entirely wanting throughout extensive 

 geological formations. But even where such fossiliferous 

 beds occur, the conditions favorable to the preservation 

 of small mammalia are exceedingly rare, the entire series 

 of freshwater Wealden beds having yielded no trace of 

 them, although we are quite certain that they were then 

 both varied and abundant. Even more remarkable is 

 the fact that the whole twenty-five species of Purbeck 

 mammals, belonging to ten genera, were obtained from a 

 single stratum only a few inches thick, and from an area 

 of less than 500 square yards. Yet these small animals 

 must have abounded at this period; and it is impossible 

 to believe that anything but a most imperfect and frac- 

 tional representation of the mammalian fauna of the 

 country could have been gathered into this narrow grave- 

 yard. But this thin stratum occurs amid a mass of 

 freshwater deposits 160 feet thick, the whole of which 

 have been thoroughly and systematically examined by 

 the officers of the Geological Survey of Great Britain; 

 and though many of the layers contain remains of land 

 organisms plants, insects, and land-shells no other part 

 of the whole series has yielded a single fragment of 

 mammalian remains! Having the striking example of 

 the worthlessness of negative evidence, it behooves us to 

 be cautious of rejecting any legitimate conclusions from 

 the facts in our possession, on account of the absence of 

 the direct evidence of fossil remains." 



From this let us turn to the other aspect of the ques- 

 tion and examine what in reality palaeontologists have 

 discovered and the bearings of that material upon biol- 

 ogy. Confessedly as meager as the number of fossils of 

 animals is that have come to light, it is so only when 

 taken in comparison with the vast host of extinct forms 

 which have as yet not rewarded the researches of science, 

 and still are hidden in the crust of the earth, or have 

 perished utterly. For, take mammals as an example, the 

 list of fossil forms now known is by no means to be de- 



