210 PROCEEDINGS OF THE AMERICAN ACADEMY 



agglomerations, and sometimes absolutely wanting over large surfaces 

 wliere the- schists only were found. 



The next step was to revisit with care the Isle La Motte, the jienin- 

 sula of Alburgh, Chazy Landing and Village, Keeseville, and Potsdam. 

 These ty[)ical localities of the Calciferous, of Chazy, Trenton lime- 

 stones, and Utica slate, already visited by me in 1849, are very rich 

 in fossils, and easy to study, and at a distance of only from three hun- 

 dred yards to one mile from the Taconic region of the eastern part of 

 Lake Champlain. "When there I saw- jjlainly the necessity of giving 

 up all idea of identifying their strata with those of Georgia, St. 

 Albans, Swanton, llighgate, and Phillipsburgh. 



Near to Chazy and Potsdam, I observed that the Calciferous sand- 

 rock, and consequently all the Lower Silurian, rested in discordance of 

 stratification on the Potsdam sandstone, — at least a discordance of six- 

 teen degrees. I had foreseen and indicated this in the additional notes 

 to the letters of Barrande in our memoir of 18G0 (On the Primordial 

 Fauna and the Taconic System, p. 380), in which I say : " I am not 

 sufficiently acquainted with its (the Potsdam group) distribution and 

 jjosition in regard to the Taconic and the Calciferous sandrocks to give a 

 decided opinion based on stratigraphical grounds, but from the descriji- 

 tion of Prof. Emmons in his Taconic system, and from what I have 

 seen at Little Falls, the Calciferous sandrocks are certainly very dif- 

 ferently distributed from tlie Potsdam, and a dislocation and disturb- 

 ance of ftrata have taken place between the two groups." 



It was a happy discover)^ for with the pala^ontological proofs of the 

 strictly primordial character of the small fossils found at Keeseville and 

 Highgate, there was no longer a doubt that the Potsdam sandstone 

 belonged to the Taconic, as the covering and last term of the Primor- 

 dial Zone in America. 



I published a letter addressed to Barrande, August 2, entitled, " Let- 

 ter to ]M. Joachim Barrande on the Taconic Rocks of Vermont and 

 Canada," with a plate of a " Comparative Tabular Section of the Upper 

 Taconic Eocks in Vermont and Lower Canada." This letter for the 

 first time mentions the existence of calcareous lentils or lenticular 

 masses of limestone in the Taconic slate, encloses the " group of Phil- 

 lipsburgh " and the "Swanton slates " between the ' Georgia slates" 

 and the "Potsdam sandstone," and contains ibo opinion that there are 

 no Calciferous sandrocks either at Phillipsburgh or at Point L^vis. 

 Finally, the calcareous lentils of Point Levis and Phillipsburgh are 

 spoken of as precursory centres, or Barrande Colonies ; Colonies of the 

 second fauna enclosed in the Prim nlial one. 



