GENERAL OBSERVATIONS. H 



not reiiuu-kable ; but it is worthy of remark that the collections from Silver 

 City and Upper Mimbres Mining Camp, with the exception of one Conchi- 

 fer, contain only arthropomatous Brachiopods and corals ; the moUuscan 

 classes Polyzoa, Onsteropoda, and Cephalopoda, and the whole subkingdom 

 Artkulata, being unrepresented. The corals belong to families common in 

 strata of that age, namely, Favositidce, CyathophjUidce, and Thecidce ; but the 

 Bi-achiopods, with the exception of one, Bhjnchonella, all belong to the family 

 StrophoinenidcB. 



Peculiar interest attaches to this discovery of strata of the Trenton 

 period in New Mexico, Nevada, and Arizona, as well as to the discoveries 

 concerning the other Lower Sllui'ian periods, from the fact that so little has 

 hitherto been known of their existence in that part of North America. 

 Indeed, with the exception of the discovery of strata of this period by 

 Jenney in Western Texas, and that of a similar one by Dr. G. G. Shumard 

 in Southern New Mexico, I am not aware that the existence of any besides 

 those here announced has been recognized in that part of the continent. 



UPPER SILURIAN. 



The collections contain no fossils of Upper Silurian age, nor has the 

 existence of any strata of that age in the region over which the explorations 

 have extended been ascertained, as far as I am aware. 



DEVONIAN. 



Among the collections are a few fossils, the locality for which is given 

 as "between San Antonio and Silver Peak, Nevada." 



All of them are too imperfect for satisfactory specific description ; but, 

 judging from their general characters, they seem to be of Devonian age. 

 The genera, so far as they are recognizable, are Favosites, Acervulariaf, and 

 Zaphrentis. There are also some fragments, probably of Atrypa retictdaris, 

 and pai't of an undetermined Trilobite. 



CARBONIFEROUS. 

 Nearly half of all the species contained in the collections are referable 

 to the Carboniferous age, mainly to its middle period Among them are 

 some very chai'acteristic fossils of the Subcarboniferous period ; but the 

 Permian has only doubtful representation. 



