246 PROCEEDINGS OF THE AMERICAN ACADEMY 



employed since 1832 by tTules Thurmann, in liis " Essai sur les Sou- 

 levements jurassiques du Porrentruy." Tluinnann, a geologist of new 

 and original ideas, was the first to recognize the utility of geographic 

 terms uniformly ending in ien, and who first used them in 1832 for 

 his very remarkable orographic classification of the Jura Mountains. 

 In 1834, pursuing the same idea, he found and employed the name 

 Neocomien, to designate the lower part of the cretaceous formation, 

 called at that time the Cretace du Jura, or Jura-Cretace. This name 

 was proposed and employed in a reunion of the Geological Society 

 of the Monts-Jura, at Besanron, on the 1st and 2d of October, 1835, 

 according to a letter that Thurmann wrote to Elie de Beaumont, which 

 the latter published in the seventh volume of the Bulletin de la So- 

 ciete Geologique de France, 1" Serie, page 209, where we read, " Je 

 (Thurmann) propose de donner le nom de terrain Neocomien (Neoco- 

 me7isis), c'est a, dire de Neuchatel comma on dit Portlandien, Oxford- 

 ien, etc." 



The coincidence of Elie de Beaumont's suggestion, in 1835, of the 

 use of the word Haxynian, with the creation of the term Neocomian, 

 which Thurmann had communicated to him, shows that the initiative 

 of these terms ending in ien or ian comes truly from Thurmann, as the 

 dates of the published documents prove. 



Sedgwick and Murchison had made a friendly association with each 

 other to study the ancient stratified rocks of England; Murchison ex- 

 ploring the grauwackes of Hereford, Radnor, and Pembroke counties, 

 while Sedgwick studied especially the slaty or scliistose region of the 

 North of Wales. The latter quickly recognized the succession of the 

 principal groups of schist, as well as the dislocations that have affected 

 them. He saw very well that his " Group of Bala" rested in discord- 

 ance of stratification on the schists of Festiniog and of Longmynd ; 

 and as no fossils had been found in the strata below the Group of 

 Bala, their thickness and their structure were not at first studied. It 

 sufficed to know that their thickness must be very great and their 

 structure very complicated, especially in the counties of Pembroke, 

 Cardigan, and Caernarvon. The attention of Sedgwick was concen- 

 trated on the Group of Bala. He recognized there a series of strata, 

 which he subdivided into two portions, containing an entire special 

 fauna. Sedgwick did not occupy himself with the study of it in 

 Shropshire and Montgomeryshire, where Murchi^on found it, and took 

 it to form his " Lower Silurian." Murchison gave as his excuse, that 

 he thought the fossils collected by Sedgwick were different from tliose 

 he had placed in his " Lower Silurian," and that he was much sur- 



