XV.] CAMBRIAN AND SILURIAN IN NORTH AMERICA. 395 



We have seen that Professor James Hall, in 1847, and again 

 in 1859, referred trilobites regarded by him as species of Olenus 

 to the Hudson-River group, or, in other words, to the summit 

 of the second palaeozoic fauna, while it is now well known that 

 they are characteristic of the first fauna. In this reference, in 

 1847, Professor Hall was justified by the singular errors which 

 we have already pointed out in the works of Hisinger on the 

 geology of Scandinavia. (Ante, page 366.) In his Anteck- 

 ningar, in 1828, while the colored map and accompanying sec- 

 tions show the alum-slates with Paradoxides to lie beneath, 

 and the clay-slates with graptolites, above the orthoceratite- 

 limestone, the accompanying colored legend, designed to ex- 

 plain the map and sections, gives these two slates with -the 

 numbers 3 and 4, as if they were contiguous and beneath the 

 limestone, which is numbered 5. The student who, in his 

 perplexity, turned from this to the later work of Hisinger, his 

 Lethsea Suecica, found the two groups of slates, as before, 

 placed in juxtaposition, but assigned, together, to a position 

 above the orthoceratite-limestone. Thus, in either case, he 

 would be led to the conclusion that in Scandinavia the alum- 

 slates with Olenus, Paradoxides, and Conocephalus (Conoco- 

 ryphe) were closely associated with the graptolitic shales ; and, 

 upon the authority of the later work, that the position of both 

 of these was there above the orthoceratite-limestones, and at 

 the summit of the second fauna. The graptolitic shales of 

 Scandinavia were already identified with those of the Utica 

 and Hudson-Eiver formations of the New York system. The 

 Red sand-rock of Vermont, containing Conocephalus, had been, 

 both by Emmons and Adams, alike on lithological and strati- 

 graphical grounds, referred to the still higher Medina sand- 

 stone ; a view which, as we have seen, was still maintained 

 and strongly defended by Adams. This was in 1847, and 

 Angelin's classification of the transition rocks of Scandinavia, 

 fixing the position of the various trilobitic zones, did not ap- 

 pear until 1854. 



Professor James Hall had therefore at this time the strongest 

 reasons for assigning the rocks containing Olenus to the sum- 



