CHAP. XX. or LOW GRADE. 401 



Next anterior in age arc the mammalia of the Lower Oolite 

 of Stonesfield, of which four species are known, also very 

 small, and probably marsupial, with one exception, the 

 Stercognathus ooliticus, which, according to Professor Owen's 

 conjecture, may have been a hoofed quadruped and pla- 

 cental, though, as we have only half of the lower jaw with 

 teeth, and the molars are unlike any living type, such an 

 opinion is, of course, hazarded with due caution. 



Still older than the above are some fossil quadrupeds of 

 small size, found in the Upper Trias of Stuttgart in Ger- 

 many, and more lately by Mr. C. Moore in beds of corre- 

 sponding age near Bristol, which are also of a very low grade, 

 like the living myrmecobius of Australia. Beyond this limit 

 our knowledge of the highest class of vertebrata does not as yet 

 extend into the past, but the frequent shifting back of the old 

 land-marks, nearlj^ all of them once supposed in their turn to 

 indicate the date of the first appearance of warm-blooded 

 quadrupeds on this planet, should serve as a warning to us 

 not to consider the goal at present reached by palaeontology 

 as one beyond which they who come after us are never 

 destined to pass. 



On the other hand, it may be truly said, in favor of pro- 

 gression, that, after all these discoveries, the doctrine is not 

 gainsaid, for the less advanced marsupials precede the more 

 perfect placental mammalia in the order of their appear- 

 ance on the earth. 



If the three localities where the most ancient mammalia 

 have been found — Purbeck, Stonesfield, and Stuttgart — had 

 belonged all of them to formations of the same age, we 

 might well have imagined so limited an area to have been 

 peopled exclusively with pouched quadrupeds, just as Aus- 

 tralia now is, Avhile other parts of the globe were inhabited 

 by placentals; for Australia now supports one hundred and 

 sixty species of marsupials, while the rest of the continents 



