Association of American Gieologists and Naturalists. 153 
Friday, April 28th.—A letter from Walter R. Johnson, E'sq. 
to the President, was read, in which he expressed his regret at 
being prevented from attending the present meeting, and enclo- 
sing his contribution towards the printing of the Transactions. 
Mr. Nicollet then read a paper ‘on the cretaceous formation of 
the Missouri River.” 
Commencing at Council Bluffs and proceeding up the river, it was 
the design to give an intelligible view of the formations exposed on the 
river banks. But, previously, for the purpose of connecting the creta- 
ceous formation with the geological formations at the east, he stated 
that the carboniferous formation could be observed from St. Louis up 
the river; that at Council BluffS and Riviere des Moines on the Missis- 
sippi, the same carboniferous fossils were found. ‘That south of the 
Missouri there was a continuation of the carboniferous and Silurian 
systems. In lowa, the representative of the Silurian system contained 
a great number of fossils characteristic of the formation, while at the 
south, the mineral region of Missouri contained none or very few fos- 
sils, and we infer that it belongs to the same system, merely from the 
mineral characters. That owing to the topographical character of the 
country, no vertical sections were exhibited. 
Mr. N. commenced his detailed observations, by giving a sketch of 
the topography of the banks of the river. The course of the river was 
continually changing—so much so that many of the bends described 
by Lewis and Clark could not now be recognized, and some laid down 
by himself on the map exhibited, in 1839, had already disappeared. He 
had, in fact, lately learned that the great bend opposite Council Bluffs, 
had been cut off. And hence it resulted that the travelling distances of 
his party, differed much from those of Lewis and Clark. Soon after 
leaving the Tchansansan, or Woody River, the hills recede from the 
banks, but after two days’ journey the river again washes their base, 
and the carboniferous limestone again appears in place. Near the 
mouth of the Sioux River, the carboniferous rocks again appear, and 
this he considers their true limit, not having met with them or any of 
the older fossiliferous rocks beyond this locality. At this place the 
rocks in the bluff, consisting of argillaceous shale and carboniferous 
limestone, were seven or eight feet in thickness. 
On reaching the Ayoway River, a great change takes place in the 
vegetation and in the geological formation of the country. At the third 
bluff above the mouth of the river, to which the name of Dixon’s Bluff 
had been given, in honor of one of his most faithful and devoted guides, 
occur a group of rocks which we called Dixon’s group. It consists of— 
Vol. xiv, No. 1.—April-June, 1343. 20, 
