WEBSTER THE ROCKFORD SHALES OF IOWA. 107 



seventy feet. It is believed that this depression was at one time entirely 

 filled by this sandstone, and subsequently eroded by the action of the 

 ice and the waters derived from the melting of it, during the glacial 

 period. 



That a better understanding of the richness of the Rockford shale 

 fauna and its relation to that of the subjacent strata may be gained, I 

 append a partial catalogue of the forms known to occur in them.* A 

 large percentage of the species enumerated have not been catalogued 

 by previous writers; but my own collection, made personally, embraces 

 all but one or two of the species listed, and these I have examined in 

 the cabinets of others who have personally collected them. 



The species followed by t occur in the rocks which underlie the 

 shales, but do not extend upward into the shales. Some of those fol- 

 lowed by ? are undescribed forms, while others occur in the form of 

 casts, making their specific identification uncertain. 



Stromatopora incrustans, H. & W. Spirorbis omphalodes, Goldfuss. 

 Stromatopora expansa, H. & W. Pleurotomaria- 



Stromatopora solidula, H. & W. Acervularia inequalis, H. & W. 



Ambonychia 1? Smithia Johanna, H. &: W. 



Caunopora planulata, H. & W. Smithia multiradiata, H. & W. 



Rhynchonella venustula,t Hall. Callonema lichas? H. 



Tellinomya ? Stromatopora alternata, H. & W. 



Fistulipora occidens, H. & W. Crania famelica, H. & W. 



Alveolites rockfordensis, H. & W. Pachyphyllum woodmani, White. 



Aulopora iowensis, H. & W. Strophodonta arcuata, Hall. 



Cladopora robusta,| Rom. Gyroceras +? 



Aulopora saxivada, H. & W. Orthoceras vastator, Hall. 



Zaphrentis solida, H. & W. Orthoceras procerus, Hall. 



Campophyllum nanum, H. & W. Strophodonta canace, H. & W. 



Aulopora ? Strophodonta variabilis, Calvin. 



Cypricardinia sublamellosa? H. Cryptonella eudora, Hall. 



Stromatopora ? Dictyonema ? 



Chonophyllum ellipticum, H. & W. Strobilocystites calvini,t White. - 



Cystiphyllum mundulum, H. & W. Spirifera ziczac,t Hall. 



Chonophyllum ? Strophonella reversa, Hall. 



Spirorbis arkonensis, Nich. Fenestella ? 



♦Aside from the species herein listed, we have in our cabinet over eighty additional forms 

 from the shales, most of which are undescrihed. 



% The individuals of this species are exceedingly rare in the shales, and constitute the only 

 representatives of the genus Cladopora yet obtained here. 



§ This species is not very abundant in the shales, and is somewhat limited in its geographical 

 range. It sometimes occurs in the limestone immediately underlying the shales. 



H This species was collected by me from the sandstone which underlies the shales, at Nora 

 Springs. It differs from the forms of this species collected at Iowa City, Iowa, mainly in 

 being somewhat larger. It is of much interest to note the wide distribution of this rare- species 

 in the Devonian rocks of this State. 



