394 CAMBRIAN AND SILURIAN I-N NORTH AMERICA. [XV. 



referred to the Potsdam group. (See, for the further history 

 of these fossils the Geology of Canada, pages 866, 955, and 

 Pal. Fossils of Canada, pages 11, 419.) 



The interstratification of the dark-colored fossiliferous shales 

 holding Olenellus with the Eed sand-rock of Vermont, an- 

 nounced by Mr. Billings, was further confirmed by Sir William 

 Logan in his account of the section at Swanton, Vermont. 

 (Geology of Canada, 281.) They were there declared to occur 

 about 500 feet from the base of a series of 2,200 feet of strata, 

 consisting chiefly of red sandy dolomites (the so-called sand- 

 rock) containing Conocephalus throughout, while the shaly beds 

 held, in addition, the two species of Paradoxides (Olenellus) 

 and some brachiopods. These beds, like those of Labrador, 

 were referred by Logan and by Billings to the Potsdam group. 

 The conclusions here announced were of great importance for 

 the history of the Taconic controversy. The trilobites of pri- 

 mordial type, from Georgia, Vermont, which by Emmons were 

 placed in the Taconic system, lying unconformably beneath a 

 series of rocks belonging to the lower part of the New York 

 system, were now declared to belong to the Red sand-rock 

 group, a member of this overlying system. Much has been 

 said of these fossils, as if they furnished in some way a vindi- 

 cation of the views of Emmons, and of the Taconic system ; a 

 conclusion which can only be deduced from a misconception 

 of the facts in the case. Emmons had, previous to 1860, 

 on lithological and stratigraphical evidence alone, called the 

 Georgia slates Taconic, and placed them unconformably be- 

 neath the Red sand-rock. If now both he and Billings were 

 right in referring the Red sand-rock to the Calciferous and 

 Potsdam formations, and if the stratigraphical determinations 

 of Messrs. Perry and G. M. Hall, confirmed by those of Logan, 

 were correct, namely, that the trilobites in question occur not 

 in a system of strata lying unconformably beneath the Red 

 sand-rock, but in beds intercalated with the sand-rock itself, 

 it is clear that these trilobites must belong not to the Taconic, 

 but to the New York, system. "VVe shall return to the ques- 

 tion of the age of these rocks. 



