WfO Mr Audubon's Observations on the 



pentiiie truly been formed at so many epochs, or must we view 

 it as we do porphyry, without any reference to the surrounding 

 rocks ? Shall we rather admit only one eruption of serpentine 

 posterior to the transition red sandstone ; or shall we give to 

 it one more ancient and anterior to the newer greywacke, or 

 even to the transition slate ? These are questions difficult to 

 be answered. It would be absurd to admit five eruptions of 

 serpentine. We are of opinion, that the formation of serpen- 

 tine is not so ancient as has been imagined, and will not in all 

 probability be far from the truth, if we limit the appearance of 

 serpentine to the great transition era, from the termination of 

 the talco-schistose deposites, to the beginning of the independent 

 coal formation. 



We may here add, that the true relations of potstone to ser- 

 pentine have not hitherto been ascertained in a satisfactory man- 

 ner. It is probable that potstone bears the same relation to 

 serpentine that schaalstein, a particular calcareous amygdaloi- 

 dal trap, does to transition trap. It is well known that these 

 last-mentioned rocks, viz. the schaalstein and transition trap in 

 Westphalia and in Cumberland, form the transition from the 

 slate or limestone to the trap, and even occur separately from 

 this last rock, and are rarely brecciated. Many geologists con- 

 found it with true amygdaloid, which generally forms the upper 

 and under parts of trap-veins, and bed-like veins and masses. 

 The schaalstone seems to be transition rock altered by the ema- 

 nation of the heat of the melted trap. If this view be correct, it 

 could be employed, in the way of analogy, in the explanation 

 of rocks associated with serpentine, and similarly situated, in 

 interrupted small masses. 



Observations on the Natural History of the Alligator. In a 

 Letter to Sir William Jakdine, Baronet, and Prideaux 

 John Selby, Esq. By John J. Audubon, Esq. Member of 

 the Wernerian Natural History Society, &c. 



My Deaii Sirs, 



One of the most remarkable objects connected with the Na- 

 tural History of the United States, that attracts the traveller's 



