372 



THE CAMBRIAN. 



|BULL. 81. 



The Lower Cambrian fauna is much more persistent in its character 

 than that of the Middle Cambrian ; for all the strata referred to the 

 former horizon have been found to be characterized by essentially 

 the same fauna. This is also true of the much more widely spread 

 Upper Cambrian with the single exception of the Atlantic Coast Prov- 

 ince, where the fauna is more of the European or Atlantic Basin type. 

 There is, however, too little known of it at present in Newfoundland 

 to base any final conclusions upon it. 



The minor or formation subdivisions of the Cambrian are based largely 

 upon lithologic characters and are relatively of local value only. One 

 exception to this is found in the " Granular Quartz " of New York and 

 Vermont, and the equivalent Chilhowee quartzite series of Tennessee, 

 Alabama, Virginia, Pennsylvania, etc. Another is in the widely spread 

 shore-line deposits, called the Potsdam sandstone in New York, the St. 

 Croix sandstone in the Upper Mississippi Valley, the supposed equiv- 

 alent deposits of the Black Hills of Dakota, the sandstones of the 

 eastern flanks of the Bocky Mountains and of the Llano area of Texas. 

 These two formations furnish illustrations of the accumulation of similar 

 sediments over very extended areas. Their minor value in classifica- 

 tion, when not supported by paleontologic evidence, is shown by the 

 fact that the Lower Cambrian "Granular Quartz" or Chilhowee sand- 

 stone has been correlated by nearly all geologists who have referred to 

 it with the Potsdam sandstone about the Adirondacks of New York 

 and the St. Croix sandstone of the Upper Mississippi Valley, thus 

 bringing together formations separated in the stratigraphic column by 

 a long time interval and several thousand feet of sediment. Other 

 sandstones of pre-Cambrian and post-Cambrian age have also been 

 correlated with the Potsdam sandstone of New York. 



With our present knowledge of the faunas and sediments it is im- 

 possible in all instances to differentiate the primary divisions of Upper, 

 Middle, and Lower Cambrian in America. 



Extending our views across to the eastern side of the Atlantic Ocean, 

 we find an extensive development of Cambrian rocks in North and 

 South Wales, where the three great divisions of the North American 

 Cambrian are to be recognized. The Lower, in the roofing-slate series 

 of North Wales and the Cserfai group of South Wales ; the Middle, 

 in the Solva and Menevian formations, and the Upper, in the Lingula 

 flags series. These divisions are also recognized in Sweden and North 

 Wales, although in greatly diminished force. The Lower division has 

 been recognized in western Russia, and the central belt of the celebrated 

 " Zone Primordiale" of Bohemia represents the Middle Cambrian series. 



Iu lithologic, stratigraphic, and paleontologic characters the Cam- 

 brian series on the opposite sides of the Atlantic are such that there is 

 no hesitancy in considering them as belonging to one geologic group 

 and as part of one geologic basin. 



There is a great variation in the sedimentation and faunas of the 



