102 THE CAMBRIAN. 



[BULL. 81. 



fossils in the Mississippi Valley, was also referred to the Primordial, 

 the review of the history of. these three Cambrian formations as they 

 appear in New York and Vermont is carried forward as that of one ter- 

 rane. 



In speaking of the determination of the age of the slates in Georgia, 

 Vermont, Mr. E. Billings states that Mous. Barraude first determined 

 their age. 1 He further says: 



At the time I wrote the note on the Highgate trilobites it was not known that 

 these slates were conformably iuterstratified with the Red sandrock. This discovery 

 was made afterwards by the Rev. J. B. Perry and Dr. G. M. Hall, of Swanton. 



He also mentions the discovery on the Straits of Belle Isle, by Mr. J. 

 Kichardson, of the Canadian Geological Survey, of 8eolithus linearis, 

 Paradoxides thompsoni, and P. vermontana, and a number of other spe- 

 cies of which a list would be given further on. He adds : 



The sandstones and limestones of the north shore of the straits [of Belle Isle] ap- 

 pear to be of the age of the Potsdam of Pennsylvania and Tennessee. The form of 

 the Scolithns is identical with that which occurs in these two States, and some por- 

 tions of the rock is a coarse red sandstone, exactly like the specimens sent to me 

 about a year ago from Tennessee by Prof. Safford. 



Mention is made of the discovery by Rev. J. B. Perry and Dr. G. M. 



Hall of a group of fossils iuterstratified with the Red sandrock east of 



Swanton, Vermont. Of the species found, four occur in the limestone 



which overlies the sandstone with Scolithus linearis on the north shore 



of the Straits of Belle Isle. 



Taking all these facts together scarcely anything more is necessary to show that 

 the Red sandrock of Vermont is of the age assigned to it by me from an examination 

 of Conocephalifces at Highgate in July last. * * * Barrande's opinion, founded 

 altogether upon the aspect of these trilobites is thus completely verified. 2 



At the close of the paper is a list of the fossils found in Vermont and 

 on the Straits of Belle Isle, all of which are referred to the Potsdam 

 group. 3 In speaking of the claim of Mr. Billings, that he had identi- 

 fied the Primordial fauna in the Red sandrock and determined its geo- 

 logical age, Prof. James Hall 4 states that he had published sections and 

 made statements in relation to the ag*e of these rocks to show that he 

 considered them to be of the age of the Potsdam sandstone of the New 

 York section. In reply Mr. Billings 5 said that the sections spoken of 

 by Prof. Hall do not cross at any point the Red sandrock or Georgia 

 slates, where they are recognized by Prof. Hall as belonging to the 

 Potsdam. On the contrary, they are marked on the section as belong- 

 ing to the Trenton-Hudson series. 



1 Further observations on the age of the red sandrock formation (Potsdam group) of Canada and 

 Vermont. Am. Jour. Sci., 2d ser., vol. 33, 1862, pp. 100-105. (See note and corrections, same vol., pp. 

 421- 422.) 



2 Op. cit., p. 102. 3 Op.cit.,p.l04. 



4 On the Potsdam sandstone and Hudson River rocks in Vermont. Am. Jour. Sci., 2d ser., vol.33, 

 1862, pp. 106-108. 



6 On Prof. J. Hall's claim to priority in the determination of the age of the Red sandrock series of 

 Vermont. Am. Jour. Sci., 2d ser., vol. 33, 1862, pp. 370-376. 



