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rormation No. 1 seems to constitute paleontologically an indepen- 

 dent division, none of its organic remains ranging in other formations 

 above or below. Nos. 2 and 3 seem to form one group_, the Ostrea 

 congesta and Inoceramas prohlematicus passing from one to the other. 

 Divisions 4 and 5, which are the most fossilliFerous formations on the 

 Upper Missouri, contain many species in common, especially of the 

 Cephalopoda, and therefore form a third group. 



The cretaceous system, as developed on the Upper Missouri, there- 

 fore forms lithologically five well marked subdivisions, while paleon- 

 tologically it admits of separation into three independent groups. 

 The age and geological position of divisions 2, 3, 4, and 5, have been 

 sufficiently attested by the numerous species of organic remains which 

 have been published, from time to time, by my associate, Mr. Meek, and 

 myself. In regard to the age of No. 1 much doubt existed, until we 

 had an opportunity to examine a fine series of Dicotyledonous leaves, 

 which I had discovered in this formation near Blackbird Hill, on the 

 Missouri, while attached to Lieutenant Warren's party, in the spring 

 of 1857. These leaves proved to us that the formation under consid- 

 eration could not be older than cretaceous, and this conclusion was 

 published by us in several of our later papers. Although the 

 evidence that it is of lower cretaceous age was perfectly satisfactory 

 to us, some writers have considered it triassic, while others have 

 regarded it as Jurassic and even miocene tertiary, in a late pub- 

 lication addressed to Mr. Meek and the writer, Professor Marcou 

 says: " Allow me respecttuUy to suggest to you that I cannot see 

 anything of cretaceous in what you call No. 1 of your Nebraska 

 section. It appears to me that you put in your No. 1, or lower 

 cretaceous, all sorts of strata of different ages, except true cretaceous 

 rocks." That the rocks in question are not newer than cretaceous I 

 will endeavor to prove, both from stratigraphical and paleontological 

 evidence. 



Evidence from stratigraphical position. 



Near the old Otoe village, on the Platte river, about five miles 

 above its mouthy No. 1 rests directly upon limestone strata of the true 

 coal measures ; and at this point I found a species oi Laurus, apparently 

 identical with a plant obtained near the mouth of the Big Sioux, and 

 at Blackbird Hill. Near De Soto, about twenty miles above Omaha 

 City, the carboniferous limestone ceases to appear, and No. 1 rests 

 with concordant stratification upon it. There is not the slightest dis- 

 turbance of the strata in this region, but they dip gently toward the 

 northwest. I traced No. 1 with great care to Blackbird Hill, about 

 sixty miles above De Soto, and found a few plants at different locali- 

 ties. At Blackbird Hill an extensive quarry had been opened to pro- 

 cure stone for building the large mission establishment at that place. 

 From this quarry I collected the fine series of dicotyledonous leaves, 

 before mentioned, I then directed my course toward the mouth of the 

 Big Sioux, about forty miles further up the Missouri, and examined 

 the country with great care. The red sandstone, No. 1, was the prin- 

 cipal rock in that region, but upon the summits of the bluffs, resting 



