OP ARTS AND SCIENCES. 243 



Stone" and the " Phyllograptus schiefer" at the base of the " Ortho- 

 ceras limestoue" by S. L. Totnquist, and referred by him to the 

 '* Tremadoc Group " of Enghxnd. The section of Vikarbyn, in which 

 the "Oio/«s-Konglomerat" and '^ Obolus-Gviiskalk " lie on the granite, 

 may offer the equivalent of the Potsdam. (See " In Ofversigt ofver 

 Bergbyggnaden in om Siljiiusomr QEdet," Dalarne, 4to, Stockholm, 

 1883.) 



If the Potsdam really exists in Europe, it is in the Iberian penin- 

 sula and in Brittany, where the sandstone of Cabo-Busto with Scolil/tiis 

 in the Astuvias (Spain), the quartzites with Bilohites of Bussaco 

 (Portugal), and the sandstones with Scolithes of Brittany (France) 

 are in the same stratigraphic position, especially in the province of 

 Caceres in Spain, and in Portugal, where the sandstones with Scolithes 

 are deposited on the Taconic schists, denuded and eroded, exactly like 

 the " Red Sandrock " of Vermont resting on the denuded and eroded 

 Taconic schists of America. 



The great dislocation of the Green Mountains drove from the 

 American regions all the types of the second fauna that had made 

 their appearance in the upper parts of the Taconic schists. Then dur- 

 ing the special deposit, limited in time and space, of conglomerates, 

 sands, and limestones that have been called " Potsdam sandstone," 

 certain characteristic primordial forms shed a last light before disap- 

 pearing forever. 



I speak especially of the trilobites, the evolution of which is easier 

 to follow than that of organisms placed lower in the scale of the ani- 

 mal kingdom. 



The dislocation that ended the Potsdam deposits ended also the 

 existence of the primordial fauna in America; and we pass suddenly 

 into the second fauna with the " Calciferous and Chazy divisions." 

 The sediments were changed, and all was prepared in the American 

 sea in which the deposit was made of the series of the " Chaniplain 

 System," or " Cambrian " proper, for the exclusive development of the 

 second fauna. 



Nevertheless, it is well to notice that as yet several animal forms of 

 the second fauna which made their first appearance in the " Phillips- 

 burgh and Swanton Groups " have never reappeared in America, while 

 they have had their complete evolution in Europe. For instance, I 

 will cite the genus Awphyx. 



And further, according to the careful palaiontologlcal researches of 

 Prof. A. Hyatt, no true Endoccras with cone in cone structure has yet 

 been found below the true " Chazy limestoue " and " Calciferous sand- 



