258 GEOGNOSY OF THE APPALACHIANS. [XIII. 



this author in his classic work, Lethaea Suecica, published in 

 1837, represents, by some unexplained error, these slates as 

 overlying the orthoceratite limestone, which is the equivalent 

 of the Trenton limestone of the Champlain division. Hence, 

 as Mr. Barrande has remarked, Hall was justified by the au- 

 thority of Hisinger's published work in assigning to the Olenus 

 slates of Vermont a position above that limestone, and in placing 

 them, as he then did, on the horizon of the Hudson River or 

 Loraine shales. The double evidence afforded by these two 

 fossil forms in the rocks of Vermont served to confirm Sir 

 William Logan in placing in the upper part of the Champlain 

 division the rocks which he regarded as their stratigraphical 

 equivalents near Quebec ; and which, as we have seen, had 

 some years before been by Emmons himself assigned to the 

 same horizon. The remarkable compound graptolites which 

 occur in the shales of Pointe Levis, opposite Quebec, were 

 described by Professor James Hall in the report of the Geo- 

 logical Survey of Canada for 1857, and were then referred to 

 the Hudson River group ; nor was it until August, 1860, that 

 Mr. Billings described from the limestones of this same series 

 at Pointe Levis a number of trilobites, among which were sev- 

 eral species of Agnostus, Dikelocephalus, Bathyurus, etc., con- 

 stituting a fauna whose geological horizon he decided to be in 

 the lower part of the Champlain division. 



Just previous to this time, in the report of the Regents of 

 the University of New York for 1859, Professor Hall had 

 described and figured by the name of Olenug two species of 

 trilobites from the slates of Georgia, Vermont, which Emmons 

 had wrongly referred to the genus Paradoxides. They were at 

 once recognized by Barrande, who called attention to their 

 primordial character, and thus led to a knowledge of their true 

 stratigraphical horizon, and to the detection of the singular 

 error in Hisinger's book, already noticed, by which American 

 geologists had been misled.* They have since been separated 

 from Olenus, and by Professor Hall referred to a new and 



* For the correspondence on this matter between Barrande, Logan, and 

 Hall, see American Journal of Science (2), XXXI. 210-226. 



