FIEST MAMMALIA. 143 



The terrestrial animals of this period were almost exclu- 

 sively oviparous, partaking largely of the sauroidal, or lizard- 

 like type, which latter remark- is even applicable to the birds. 

 Toward the close of the period, however, an animal appeared 

 which may be regarded as a transition link between the 

 oviparous and viviparous. It was an animal of the class Mar- 

 supialia; in other words, an animal with a pouch, like that of 

 the opossum, or kangaroo, in which it sheltered and nour- 

 ished its young for a season after their birth, the same 

 being yet too feeble and imperfectly developed to endure 

 exposure to the outer elements. It has hence been remarked 

 that, " though the young of this animal were born alive, they 

 were only half born, as it were," and needed a kind of sup- 

 plementary gestation to fit them for- life in the external 

 world. 



Like the fifth development or member of every other seven- 

 fold series, therefore, this is characterized by the assumption of 

 distinctness, or partition, in forms and gradations of forms, 

 from a state of previous and comparative indistinctness. The 

 principle of segregation is here distinctly observed, the same 

 as it was in the fifth stage of the universal creation. Each 

 one of these forms, being yet transitional and incomplete, is, 

 as it were, a nucleated point in the previously chaotic materials 

 and their involved principles ; and therefore the whole devel- 

 opment, being the second of the Secondary Trinity, has a cer- 

 tain correspondence to the second of the Primary Trinity, 

 which was characterized by a nucleation of the materials of 

 the earth as a whole. 



6. The SIXTH stage of the earth's formation was comprised 

 in the whole period commonly termed the Tertiary and Dilu- 

 vial periods. It commenced immediately after that remark- 

 able marine, terrestrial, and atmospheric change which must 



