1392.] Geology and Paleontology. -41 



may be considered identical; while & Wtnetfus from the Calcitonins 

 and S. woodii from the Upper Cambrian of the MissiflBppi Valley may 

 be said to be separable by no definable characters. S. dchcatuhis 

 from the Cincinnati differs from S. minmtm only in having the caviti. s 

 of the tubes filled instead of being hollow. Finally, S. minneaoUntit 

 from the St. Peter is the same, so far as characters go, as S. linearis 

 from the lower Cambrian. 



It cannot be considered as at all probable that the annelid living in 

 the lower Cambrian and making the perforations we know as N. linea- 

 ris persisted in the same form through all later geological pen. ds into 

 Triassic time. Mr. Walcott does not think it probable that the same 

 species ranged even through Cambrian time, to say nothing of a much 

 greater time-range. Yet he places forms from the lower and Aon the 

 upper Cambrian under the same specific name. On the same principle 

 we should unite all the species, in whatever geological horizon they 



one* from another. But this does not seem advisable, and under the 



decide the name to be used. Thus, 8. linearis might be applied to 

 forms from the lower Cambrian rocks of the eastern United States ; S. 

 canadensis to those occurring in upper Cambrian strata of the eastern 

 United States, and S. woodii to those from strata of similar age in the 

 upper Mississippi Valley ; S. minutus might be the name for the form 

 in Calciferous strata: S. minnetoteima might be applied to the forms 

 from the St. Peter, and S. delicatulus to those in Cincinnati rocks; 

 S. dintonensis might be applied to those from Clinton and Medina 

 strata, S. verticalis to those from the Portage, and S. shepardn to those 

 from the Triassic. It is probable, also, that a name should be given 

 to forms collected from other horizons, say S. arizomcus to the form 

 from the Grand canon in Arizona. 



Several objections may be urged against such an arrangement. 



3 of all value as indicating the age 



:h 



nother. This i 



One of these is that it rol 



of the rocks in which it occurs. This is true. It depr.ves &0&/A**, 



too of any value as a means of correlating rocks of I 



t can be brought forward to justify placing the rocks of 

 ■ ' -ie upon the evidence of 



two widely separated areas in tne same ceriai 

 such a form as Scolithus—a. form of indefinite 

 features, of perplexing variability, and of wn 

 of forms of this sort as a means of correlatioi 

 use of lithological characters. Time does nc 



permit men 



