GENEKAL OBSEKVATIONS. 13 



region is a matter of considerable importance, I give the following detailed 

 statement of the relations of these fossils to the typical fauna of the period, 

 and especially to that of the epoch to which I have referred them. It is 

 well known that in America several species of fossils are known to range 

 through all the formations of the Subcarboniferous into those of the Car- 

 boniferous period, especially into the limestones of the latter. The discovery 

 of any of these species alone in any given strata would not, therefore, enable 

 us to refer the strata containing them to one of these periods rather than the 

 other. On the other hand, certain genera occur in strata of each one of 

 these periods that are not known to occur in the other, in which latter case 

 the generic character becomes of greater value than the specific in the foniier. 

 It is upon evidence of the latter kind that I have referred the fossils of the 

 three localities named to the Subcarboniferous period. 



The following list contains the names of the genera represented in the 

 collections from those localities : — 



Favosites. Syringopora. 



Granatocrinus. Zaphrentis. 



Platycrinus. Productus. 



Adinocrinus. Hemipronites. 



Strophomena. Orthis. 



Spirifer {Syringothyris type). Spirigera. 



Conocardium. Spirifer (Trigonotreta type). 



Terebratida {Bielasma). 

 Enomplialus. 

 Those genera of the left-hand column are not known to occur in strata 

 of later date than the Svibcarboniferous, wliile those of the right-hand column 

 are known to range both above and below it. The generic value of the 

 latter genera in this case is only to add weight to the evidence afforded by 

 the others, which is of itself, however, very decisive. Here are seven genera, 

 that are known to occur in Subcarboniferous strata elsewhere, but are 

 known in no strata of later date ; and as they are found at the localities 

 named associated with types peculiar to the Carboniferous age, the propriety 

 of refen'ing the species which represent those genera in the collections to the 

 Subcarboniferous period seems unquestionable. 



