GENERAL OBSERVATIONS. 9 



The discovery derives additional interest also from the fact that the period as 

 such, and as distinct from the Primordial on the one hand and the Trenton 

 on the other, has not, until lately, been fully recognized. 



So far as known to me, neither the Calciferous nor Chazy formation of 

 this period has been recognized in connection with the Quebec strata referred 

 to, nor indeed anywhere in the Rocky Mountain region. It is too early to 

 say or suggest what bearing this fact may have upon the opinion iinder- 

 stood to be entertained by the Canadian geologists that the Quebec strata 

 are deep-sea representatives of those of the Calciferous and Chazy forma- 

 tions. 



TRENTON PERIOD. • 



The localities at which fossils belonging unquestionably to the Trenton 

 period have been collected are Silver City and Upper Mimbres Mining- 

 Camp, N. Mex. A few other species have been collected at other localities 

 in Arizona and Nevada, which localities are more specifically designated in 

 connection with descriptions of the species on following pages. These 

 species I have also referred to the Trenton period, but the intrinsic evidence 

 they afford as to their stratigraphical position is not so entirely satisfactory 

 as that presented by the collections from the two first-named localities. 

 Besides all these, four species of Graptolites were collected from partially 

 metamorphosed shale near Belmont, Nev. No other fossils were found 

 associated with the Graptolites that might aid in indicating their exact strat- 

 igraphical position ; but I have referred them provisionally to the same 

 period with those already mentioned. 



As regards the epochs of the Trenton period to which the fossils of 

 these localities respectively belong, those from Silver City and Upper 

 Mimbres Mining Camp are referred without hesitation to the Cincinnati 

 epoch. This is done not only because of the general similarity of faunal 

 characteristics, but also because of the identification of four species from 

 the strata there that are characteristic ones of the strata of that epoch at 

 the typical localities. The four species referred to are Favistella stellata 

 llall, Stroplwmena filitexta Hall, OrtMs biforata Schlotheim (var. h/nx), and 

 0. occidentalis Hall. 



