289 



Observations upon the Rocks of the Mississippi Valley 



WHICH HAVE been REFERRED TO THE ChEMUNG GrOUP OF 



New York, together with Descriptions of New Species 

 OF Fossils from the same,horizon at Burlington, Iowa. 

 By C. a. White and R. P. Whitfield. 



The fossils from which the following descriptions are drawn were 

 all collected at and in the vicinity of Burhngton, Iowa, from the lower 

 beds there, which have been referred to the Chemung group of New 

 York. 



A part of them have been for some years in the cabinet of C. A. 

 White ; the others were collected under the direction of Prof. James 

 Hall, the State Geologist of Iowa, and on account of the geological 

 work of that State. This work having been temporarily suspended, 

 Prof. Hall has kindly placed these fossils in our hands for description. 



The following general remarks are also, in part, the result of obser- 

 vations made while pursuing some geological investigations under his 

 direction, the final results of which will appear in his fourth volume of 

 New York Paleontology. 



Discussions as to the geological equivalency of these rocks with those 

 of the Chemung group of New York having been lately renewed,* it 

 seems necessary for us, in referring our species to theii' proper horizon, 

 to offer some general remarks upon the subject. 



The Hamilton group of New York presents us with not only decided 

 Devonian characters, but also a reliable horizon in its extension west- 

 ward, as seen at various points in Illinois and Iowa. This horizon is 

 referred to and regarded by all as being reliable, and as being of De- 

 vonian age. Several species of fossils in this formation are abundant, 

 and have a wide geographical distribution, which renders it compara- 

 tively easy to recognize it in all its lithological changes. The fossils 

 referred to are principally Brachiopoda, which are usually in a much 

 better state of preservation than others, which adds still more to the 

 facility of identifying species. 



On the contrary, the Chemung group of New York, which overlies 

 the Hamilton group, presents many and sudden changes in its pale- 

 ontological characters, even within the limits of that State, and as we 

 pass westward into Pennsylvania and Ohio these changes become 

 very marked, even when we are able to trace the strata in direct con- 

 tinuity. 



In north-eastern Ohio we have so far been able to recognize few, if 

 any, of the species as common to the corresponding strata of New 



* See F. B. Meek and A. H. "Wortlien, on tlie ag-e of tlie Goniatite Limestone 

 at Kockford, Indiana, in American Journal for Sept., 1861^ also note by the 

 editors, page 288. 



PROCEEDINGS B. S. N. H.— VOL. VIH. 19 FEBRUARY, 1862 



