590 DISCOVERY OF FOSSIL VERTEBRATA. [Ch. XXVII. 



Britain being still the only country in the world in which mammalia 

 have been found in oolitic rocks. And if geology had been culti- 

 vated with less zeal in our island, we should know very little as yet 

 of two extensive assemblages of tertiary mammalia of higher anti- 

 quity than the fauna of the Paris gypsum (already cited as having 

 once laid claim to be the earliest that ever flourished on the earth) — 

 namely, first, that of the Headon series (see above, p. 284), and, sec- 

 ondly, one long prior to it in date, and antecedent to the London 

 Clay. This last has already afforded us indications of Cheiroptera, 

 Pachydermata, and Marsupialia (see p. 292). How then can we 

 doubt, if the globe were to be studied with the same diligence, if the 

 six great continents, Europe, Asia, Africa, North and South America, 

 and Australia, were equally well known, that every date assigned by 

 us in the above Table for the . earliest recorded appearance of fish, 

 reptiles, birds, and mammals, would have to be altered and shifted 

 back % Nay, if one other area, such as part of Spain, of the size of 

 England and Scotland, were subjected to the same scrutiny (and we 

 are still very imperfectly acquainted even with Great Britain), each 

 class of vertebrata would perhaps recede one or more steps farther 

 back into the abyss of time; fish might penetrate into the Lower 

 Silurian — reptiles into the Upper Devonian — mammalia into the 

 Lower Trias — birds into the Middle Oolite — and, if we turn to the 

 Invertebrata, Trilobites and Cephalopods might descend into the 

 Lower Cambrian — and Foraminifera into rocks now styled Azoic, and 

 older than the Lower Laurentian. 



Yet, after these and many more analogous revisions of the Table, 

 the order of chronological succession in the different classes of fossil 

 animals would probably continue the same as now ; — in other words, 

 our success in tracing back the remains of each class to remote eras 

 would be the greatest in fishes, next in reptiles, and least in mamma- 

 lia and birds. 



We have of late years acquired striking proofs of the difficulty of 

 detecting the bones of man in those strata in which the works of 

 his hands in the shape of flint implements abound. There are also 

 large tracts of Eocene rocks very prolific of shells and other organ 

 isms, as in Belgium, for example, which have been diligently studied 

 for nearly a century without yielding a single bone of a mammifer. 

 In the whole world the cretaceous and oolitic rocks have each of 

 them only afforded as yet a single example of a fossil bird. It would 

 almost seem as if the higher the type of organization the more pow- 

 erful the spell required to evoke the remains of a fossil being from 

 its stony sepulchre. 



" Unwilling I my lips unclose — 

 Leave, oh ! leave me to repose." 



That we should meet with ichthyolites more universally at each 

 era, and at greater depths in the series, than any other class of fossil 



