474 



GEOLOGY. 



latter were the first known barnacles of the modern sessile type. In 

 losing its pedicel, and in fixing itself immovably on other objects, it 

 became a degenerate type, but it found an unworthy place for itself 

 to which it has hung with wonderful persistency, not unlike the debased 

 human class which it has come to typify, for it has lived through all 

 the ages since, and still shows no signs of extinction. 



The Northwestern Hamilton Fauna. 



While the preceding fauna was developing in the eastern interior 

 sea and apparently receiving contributions from more southerly coasts, 

 another fauna was evolving on somewhat different lines in a sea that 



•e 







s 



D 



M 



P 



P- 



T 



j 



jC 



K 



T^r 









A 























70/ 



\ 





















A 5 - 



, 



' \ 



















// 



f / 



/ 

 t 



so 



\ 











> — $4 









Zdf 









1 

 \ 

 \ 

 \ 



\ 

 \ 







Im. 



1 1 

 ' 1 





s 



v^/ 



^20 











\ 



-.£ 











^€,^ 



"'"'---.* 



Fig. 211. — This curve is compiled chiefly from data contained in Schuchert's 

 Synopsis of American Fossil Brachiopoda, and represents approximately the 

 state of our present knowledge of the geologic range of the genera of fossi] 

 Brachiopoda. The broken line represents the number of new genera initiated during 

 the successive geologic periods ; the full line represents the total number of genera 

 present; and the difference between the two represents the number of genera 

 which have passed over from the preceding period. 



appears to have overspread a large tract in the northwestern interior. 

 This sea embraced portions of Missouri, Iowa, Manitoba, and the 

 Mackenzie valley. It doubtless had its oceanic connection at the 

 north or northwest. It does not appear to have had any connection 

 with the ocean to the south in the earlier stages. It seems to have 



