the Upper Devonian of Iowa. 375 



bottom, persisted in some congenial localities at present 

 unknown, suffering in the meantime only a very slight 

 amount of modification, and again appeared, reinforced 

 by a number of other species, when the sea bottom offered 

 conditions favorable to its success.' ' (la. Surv. VII, 

 pp. 169-170.) 



Even if the actual connection between the Hackberry 

 and Independence faunas were as close as Calvin thought 

 it to be, this theory of the origin of the Hackberry would 

 be rather far-fetched. But upon examination of series 

 of Independence material it will be found that even in 

 those species that are common to both formations there 

 is considerable variation in form. This variation may 

 be of merely varietal importance, as in Productella hal- 

 lana Walcott, or it may be of such importance that spe- 

 cific separation would be justified and desirable. In 

 general it may be said, therefore, that the connection 

 between the Independence and the Hackberry — one based 

 at best on less than fifteen species — is too small to be of 

 any importance. 



In the case of the High Point beds there is probably 

 more evidence of f aunal connection, as shown by Clarke 

 in Bulletin 16 of the U. S. Survey, though at best the 

 number of species (following Clarke) is not above six- 

 teen or seventeen. When this number is compared with 

 the not less than two hundred-fifty fossil forms to be 

 found in the Hackberry, the futility of any attempts at 

 correlation of the two formations may be easily seen. 

 As the supposed relationship with the Independence was 

 one of faunas only, without attempt or possibility of cor- 

 relation, it is apparent that the Hackberry is a separate 

 and distinct stage, with no known equivalent. 



The age of the Hackberry has been variously given as 

 Hamilton, Portage, Chemung and even as Kinderhook. 

 Actually it is of the latest Devonian age, of the Chautau- 

 quan series, and is the most recent of any of the Devo- 

 nian formations of the Dakotan province. "Webster 

 regards it as being of practically the same age as the 

 Ouray limestones of the west; indeed he regards the 

 latter as laid down by another division of the same body 

 of water that developed the Hackberry. The extent of 

 the Hackberry, previous to erosion, is of course unknown. 

 In all probability, however, it was much greater than is 

 now indicated by exposures. 



