86 GEOLOGICAL SURVEY OF THE TERRITORIES. 



Eivers some yellow and buff magnesian limestones occur, which are sug- 

 gestive of permian relations, but it is quite doubtful whether rocks of 

 that age extend up into Nebraska, although they occur in Kansas. On 

 my geological map I have usually colored a small strip of permian 

 extending up into Southern Nebraska, but our present knowledge would 

 indicate that it might be omitted. Although some of the fossils seem 

 to possess permian affinities, they all extend down into the coal measures, 

 and therefore are not peculiarly characteristic. As we have before re- 

 marked, the carboniferous rocks along the Missouri River are immediately 

 overlapped by formations of cretaceous age. These rocks as revealed 

 along the Missouri, have been separated into five well-marked divisions, 

 which have been designated by numbers 1, 2, 3, 4, .and 5, and by groups, 

 as Dakota Group, Fort Pierre Group, and Fox Hills Group. Inasmuch 

 as we shall have occasion to refer to these groups in describing rocks in 

 the cretaceous epoch in other portions of the West, we will introduce here 

 a general section of the cretaceous rocks along the Missouri Elver, as pre- 

 pared by Mr. Meek and the writer several years since, and published in 

 previous reports. There are so many students of western geology 

 scattered over the country at the present time, most of whom cannot 

 gain access to the memoirs in which these sections have been pub- 

 lished, that this will be a sufficient reason for reproducing them in 

 this connection. Not only in this report, but also in subsequent reports, 

 we shall have constant occasion to refer to these sections, and the differ- 

 ent groups of rocks. The sections were based on characters obtained 

 from a careful study of the groups as exposed along the Missouri Eiver, 

 and it is here that their typical characters are found. As we depart 

 from this center in any direction these characters are modified more or 

 less. As we go southward into the Laramie Plains, Colorado, or New 

 Mexico, these divisions are not as well defined, and Drs. Newberry and 

 Leconte have very properly divided the whole cretaceous group, as 

 there developed, into upper, middle, and lower cretaceous. Yet, to 

 one familiar with the typical divisions as seen on the Upper Missouri, 

 geographical extension never modifies them so that they do not still 

 possess some traces of their original characters. 



Formation No. 1, as seen all along the flanks of the mountains from 

 the Big Horn and Wind Eiver ranges to New Mexico, has never yielded 

 a single characteristic fossil, and the lithological characters are quite 

 different in many respects from those which are peculiar to the group, 

 as shown near Sioux City and southward into Kansas. Again, in their 

 southward extension, the division into upper and lower cretaceous 

 groups would probably best accord with the facts as we know them at 

 the present time. 



