OF ARTS AND SCIENCES. 233 



this group does not seem to show the types prophetic of the second 

 fauna, so remarkable at Phillipsburgh. 



For Messrs. Walcott and Hague, the Cambrian ends with the 

 " Hamburg shale," without a break in the stratification and without a 

 well-marked palteontologic horizon, since the species pass into the 

 higher group which they call " Pogonip limestone." These savants 

 have been influenced by the apparition of forms of the second fauna, 

 and place themselves at a point of view entirely pala3ontologic, 

 although quite open to discussion, even palteontologically. They have 

 drawn there a strong line of separation between two geologic ages, 

 which they call '• Cambrian " and " Silurian." 



The " Pogonip limestone," 2,700 feet thick, gradually passes into 

 the " Hamburg shale" in concordant stratification, and contains a fine 

 fauna, a decided mingling of species of primordial and second fauna 

 forms, exactly the same as at Hof in Bavaria, and at Christiania, 

 Norway. Mr. Walcott gives a list of sixteen species which he recog- 

 nizes as common here and in the beds beneath, which he calls 

 " Cambrian." They are Dlkelocephalus, Crepicephalus, Arethusina, 

 Agnostus, Acrotreta^ Obolella, Lingida^ and Lingidepis. 



Towards the middle of the " Pogonic group " are found Bathyurus, 

 Amphio7i, Asapkiis, lUcenns, 3Iaclurea, Orthoceras, Ort/n's, etc. All 

 these forms exist at Point Levis, Phillipsburgh, and Highgate Springs ; 

 and at Eureka and in Nevada we have the same mixture and the 

 same associations as in Vermont and Canada. 



One single Graptolites has been found in Nevada, and it is in the 

 " Pogonip group." 



By its position above the beds with Dikelocephalus of the " Ham- 

 burg and Prospect Mountain Groups," and its mixed fauna, it is evi- 

 dent that here are the Colonies of the second fauna in the primordial 

 fauna, as in the " Swanton slates " of Lake Champlain ; and I do not 

 hesitate to consider the " Pogonic limestone " as representing in Ne- 

 vada the " Swanton slates." 



Above we have the " Eureka quartzite," 500 feet thick, in which, 

 unhappily, as yet no fossils have been found ; but we must remember, 

 that many years had passed before the discovery of the small Cono- 

 cephalites Adamsi and C minutus at Highgate and at Keeseville, 

 and that we may hope for a like success at Eureka. In position and 

 lithology the Eureka quartzite recalls the '• Red Sandrock" of Vermont 

 and the " Potsdam " of Keeseville, ChazyJ" and Potsdam. Further, 

 although Messrs. Hague and Walcott have not recognized a discord- 

 ance between this group and the "Pogonip," the excellent Geological 



