THE OPOSSUM 59 



But that time was, after all, only in the tertiary period, 

 and a " tertiary " family can have but a mushroom 

 antiquity in the eyes of a creature which can establish 

 its claim to have had ancestors in a flourishing condition 

 during the secondary epocli. Yet this is just what the 

 little myrmecobius can do. Its congeners even then 

 lived in England, as is proved by the fact that their 

 relics have been found in the Stonesfield oolitic rocks, 

 the deposition of which is separated from that which 

 gave rise to the Paris tertiary strata, by an abyss of past 

 time which we cannot venture to express even in 

 thousands of years. We have, then, in Australia what 

 may be termed a surviving oolitic land, still showing us, 

 in the present day, a living representative of forms 

 which once indeed dwelt in the north, but have long 

 since passed away from among us, leaving but rare and 

 scattered relics " sealed within the iron hills." 



When we pass from secondary and tertiary strata to 

 deposits comparatively modern, we find that creatures 

 closely allied to the kangaroo existed in Australia in 

 times which must be called ancient historically, though 

 very recent geologically. Just as in the recent deposits 

 of South America we find the bones of large beasts, first 

 cousins to the sloths and armadillos which exist there 

 still, so in Australia there lived beasts having all the 

 more essential structural characteristics of the kangaroo, 

 yet of the bulk of the rhinoceros. 



But, while we are speaking of fossils, we may mention 

 an interesting circumstance which occurred with respect 

 to the Paris predecessor of the American opossum found 

 by Cuvier in the quarries of Montmartre. He first laid 

 bare a lower jaw, and from a character it possessed — 

 which is common to marsupial animals generally — he 

 predicted that when the rest of the skeleton was 



