16 



Upper Carboniferous. 1 On this subject Dr. Hayclen remarks 2 that "It is 

 very difficult to find rocks of this Dakota group resting immediately upon the 

 beds below, from the fact that in almost all cases a grassy slope intervenes ;" 

 that "it became a matter of much importance to find the junction of the two 

 great formations or to ascertain what beds come between." For my explora- 

 tions of 1873 over part of the area of the same group, I was therefore directed 

 by Dr. Hayden to carefully look to exposures where the strata positively 

 referable to the Dakota group could be seen in immediate connection with 

 those of the underlying or overlying formations. Before exposing the result 

 of my researches on this point, I will record here again the only case of im- 

 mediate superposition discovered by Dr. Hayden, and published a long time 

 ago. 3 The observation was made near the old Otoe Village, about eight miles 

 above the mouth of the Platte River. " The section, in descending order, is 

 as follow : 



" 1. Gray, compact, siliceous rock, passing down into a coarse conglom- 

 erate, an aggregation of water-worn pebbles cemented with angular grains 

 of quartz ; then a coarse-grained micaceous sandstone, 25 feet. 



"2. Yellow and light-gray limestone of the coal measures, containing nu- 

 merous fossils — Spirifer cameratus, Athyris subtilita, Fusulina cylindrica, with 

 abundant fragments of coral and crinoid remains, 20 to 50 feet. A, quartz 

 rock; B, conglomerate; C, coarse micaceous sandstone; D, Carboniferous 

 limestone." 



With the clay beds generally at the base of the Dakota group the series 

 marked by letters resume, as will be seen, the essential lithological character 

 of the strata of the group. 



Having recognized the connection, as marked above, along the Platte, I 

 found in Gage County, near Beatrice, about eighty miles more southward, 

 along the banks of the Big Blue River, some exposures of the same kind, 

 where the strata of the limestone, with those of the Cretaceous sandstone 

 above, could be seen either in close or in immediate conjunction. 4 The 

 variety in the nature of the lowest strata is at first seen at many places. Near 

 the base of the group, beds of fine soft plastic clay, either white or, more 



1 The question of the relation of the Dakota group to European groups of the Cretaceous, as con- 

 sidered from analogy of vegetable remains, is discussed after the description of the species. 



2 Report of 1867, p. 42. 



3 Transactions of the American Philosophical Society, 1862. 



*Dr. Hayden had previously visited the same country, and recorded about the same observations. 



