14 DAVENPORT ACADEMY OF NATURAL SCIENCES. 



OUR LOCAL GEOLOGY 



BY W. H. BARRIS 



INTRODUCTORY AND EXPLANATORY. 



In former papers on our Local Geology, the author treated of the 

 discovery, character, and contents of the lowest series of fossiliferous 

 rocks here exposed on the Mississippi River. 



They had been necessarily overlooked in the earlier (Geological sur- 

 veys of the State, inasmuch as they had not been discovered until 

 after those surveys were comi)leted. Lithologically they seemed dis- 

 tinct from any of the rocks witii which they were here associated. 

 Their more characteristic fossils were new and undescribed, differing 

 widely from any of the forms above them. It was acknowledged they 

 underlaid what was considered the western extension of the Hamilton 

 Group of the New York geologists. From these they seemed widely 

 separated. There was a difference in rock structure apparent at a 

 glance. Fossils were new, some having an external resemblance to 

 those of the Corniferous. The api)earance of certain corals and the 

 presence of a coral-reef suggested such reference. 



It was not simply an' individual caprice or fancy that led to such 

 identification. The highest authorities in both Iowa and Illinois 

 geology had plainly and fully expressed their opinions. Professor 

 Hall had traced the rocks of the Upper Helderberg through and be- 

 low the city, had defined their position in Rock Island as underlying 

 the Hamilton.* Professor Worthen considered them to be most nearly 

 allied to the Hamilton of New York, and yet claimed they contained 

 some fossils that in that State were characteristic of the Upper Helder- 

 berg. Hence, his conclusion was that they were really the western 

 representatives of both these formations. f In view of such facts, and 

 in deference to such authority, the local workers in the rocks naturally 

 came to the conclusion that both the Upper Helderberg and Hamilton 

 were here represented. That such conclusion was not altogether sat- 

 isfactory is made evident by the fact that in neither of the three col- 



* Geology of Iowa, Vol. L, page 86. 

 t Geology of Illinois, Vol. L, page 120. 



