GEOLOGICAL AXD XATURAT, HISTORY SURVEYS. 87 



With the exception of severjil excursions into the interior in order to trace 

 out more fully some of the formations, my whole time was expended in the 

 investigations along the Mississippi River. I have examined with care all 

 the exposures of rock from the northern line of the State to the mouth of the 

 Des Jloines River, and I have the materials for constructing a well-deflned 

 section of the rocks along this whole line. This section will he the ground- 

 work for all future operations in the interior of tlie State and is very im- 

 portant as preliminary progress in the survey. The limits of each formation 

 along the river line are now well ascertained, as also the character and order 

 of succession among the different beds, giving us greater facility and certainty 

 In tracing the continuation of the same formations into the interior of the 

 State wlien the great accumulation of drft material often obscures the under- 

 lying rocky strata. 



During this investigation I have been able to prove the existence of several 

 rock formations not before known in the State, though well known in New York 

 and elsewhere. The facts thus ascertained will show that the geological sei-ies 

 in Iowa is much more complete than had heretofore been supposed, and it 

 places us at once in the position to make comparisons between its geology and 

 the geology of other portions of our country which have been accurately studied. 



The lowest rock which I find in Iowa on the Mississippi River is that known 

 as the Potsdam sandstone, being the lowest fossil-bearing rock in the known 

 world. This rock ^^ ith all those above it dips beneath the level of tlse river 

 as we descend the stream, admitting an examination of all the beds in succes- 

 sion as they descend to the river level. 



The formations thus recognized in their ascending order are the Potsdam sand- 

 stone, Calciferous sandstone (lower magnesian limestone of Owen) ; the sand- 

 stone of the Chazy period; the Birdseye, Black River, and Newton limestones; 

 the Galena limestone; Hudson River group; Niagara limestone; a group of 

 limestone beds above the Niagara limestone requiring a new designatitm. The 

 Onondaga salt group; the lower Helderberg limestones; the Hamilton group; 

 the Chemung group; the Biu-!ington limestone; the cherry beds of the Lower 

 Rapids; the Keokuk and Warsaw limestones. The latter are succeeded by the 

 Coal Measures of lov/a, which occupy much of the southern and central por- 

 tions of the State. 



The small area of coal measures which begins above Davenport and extends 

 to below Muscatine along the river is but a narrow and interrupted belt, and 

 has no connection witli the series of coal measures which occupy the interior of 

 the State. 



The Burlington and Keokuk limestones belong to the series termed "Car- 

 boniferous limestones," as well as some succeeding beds not seeu at Keokuk. 



As there existed much confusion in regard to the Carboniferous limestones, 

 as elucidated in the report of this part of the country, I found it necessai-y to 

 trace these formations some distance south of the limit of Iowa, when they 

 become more fully develoiied and the facilities for studying their relations are 

 more favorable. Conse<iuently, after the season had so far adv:inced that I 

 could no longer work in the State I carried forward my investlgati(ms to the 

 southward, v.ith the most gratifying results. These results I shall give in 

 detail in the repoi*t hereafter to be made, and I flatter myself that it may not 

 be without interest to the people of Iowa, as I fee! sure that it will be regardesl 

 as of the greatest interest to the science of geology. 



Mr. Whitney has devoted his time mostly to the lead region in the vicinity of 

 Dubuque and will be prepared to communicate next year some valuable informa- 



