STATE GEOLOGIST. Ill 



Of the fifty-five species discriminated in the foregoing list, 

 only sixteen have been even doubtfully identified with species 

 hitherto described. Of these sixteen, twelve only are known 

 to the writer to occur in the carboniferous rocks of the Western 

 States, and are distributed as follows: 



In the Coal Measures: Produclus Wilberanus (?). 



In the Kaskaskia Limestone: Produclus pileiformis, Athyris 

 subquadrata, A sublamellosa Terebratula subretziosforma (?) AUo- 

 risma clavata. 



In the St. Louis Limestone: Lithostrolicm mammillare, Pro- 

 duct u a AUonensis, Spirifer Keokuk, var. Also the Fenestella, 

 No. 239, 



In the Keokuk Limestone: Cyathophyllum fungitesf?) 

 ■' In the' Carboniferous Limestone generally: Orlhis umbracu- 

 lum. 



In the present state of our knowledge, it would be prema- 

 ture to attempt to identify the Carboniferous Limestone of 

 Michigan with any of the group of Illinois and neighboring 

 States. Attention may, however, be directed to the following 

 points : 



1. No indications of Archimedes have been detected in the 

 formation. 



2. Very few indications of Encrinites have been discovered. 



3. The probable identification of five species, with forms be- 

 longing* to the Kaskaskia Limestone, affords a pretty strong 

 indication that at least some parts of our formation lie in the 

 horizon of the very top of the general series. 



4. The identification of lour species with forms from the St. 

 Louis Limestone, foreshadows a strong affinity with that part 

 of the system. The brecciated character of many portions of 

 the rock, points, if anywhere, to the same relationship. 



5. The ferruginous, arenaceous stratum, occurring in the 

 midst of the formation, may easily mark the boundary line be- 

 tween the twe successive epoehs last mentioned ; although, at 

 present, it is impossible to say whether the distribution of the 

 fossils conforms with such a separation. 



