May, 1845.] 235 



To Professor Henry D. Rogers, Samuel George Morton, M. D., and Pro- 

 fessor Waller R. Johnson, Committee of Ike Academy of Natural Sciences 

 of Philadelphia. 



Gentlemen, — A plain statement of such facts as I have been able to collect 

 in reference to the Geological character of the country bordering on the Mis- 

 souri River, will perhaps be preferable to attempting a detailed reply to the 

 questions proposed by your Committee to Mr. Audubon and myself on our de- 

 parture for the upper waters of the Missouri in the spring of 1843. I would 

 beg leave to remark that our opporlunitics for Geological research fell far short 

 of our anticipations. The extent of our journey was unexpectedly limited to 

 the mouth of the Yellowstone, and just before leaving that place, a diagram, 

 which I had found of the strata in the hills rising back of Fort Union, was un- 

 fortunately destroyed when too late to replace it. The specimens taken from 

 these strata will be found in the box which I have sent to the Academy. Our 

 opportunities in descending the river were also far from being favorable. Fre- 

 quent storms and high winds obliged us to lie by in places which we would not 

 have chosen for any of the purposes of the expedition, so that by taking advan- 

 tage of all the good weather to hasten our progress, we were only able to reach 

 St. Louis in our Mackinaw boat on the sixty-third day from Fort Union. 



In the whole course of the Missouri, from its mouth to the mouth of the Yel- 

 lowstone, the strata are horizontal, and as we passed up the River, I noted the 

 points at which each of the principal series was lost under the water by the 

 rise in the bed of the stream. Thus — the lower series of secondary limestone 

 disappears a few miles above Bellevue, and at Cabaue's Bluff, twenty miles fur- 

 ther, a ledge of rocks crosses the river beneath the water, causing a slight rapid 

 at a low stage water. I take this to be the last evidence of that formation. 

 From Cabaue's Bluff to the Grand Sioux River, a distance of about 160 miles 

 the River approaches the Bluffs in but few places, and in those places the rock, 

 of about 60 feet in thickness, appeared to be a soft sandstone. (In no part of 

 this formation had we an opportunity of landing to ascertain the nature of the 

 rock, still I thought we were near enough to pronounce it sandstone.) This 

 stratum loses itself in the River near the Grand Sioux. At this place a stratum 

 of soft clay stone appears, which runs to within a few miles of the lower end 

 of the Great Bend where there is another submerged ledge of rocks crossing the 

 River. Then we have Nicollet's great bed of clay which is visible until you 

 pass the Mandans, terminating between Beaver and Grand Rivers. Here com- 

 mences what 1 have called the Yellowstone series, which probably continues to 

 the great Falls of the Missouri, or until it is met by the outcropping rocks of the 

 mountain range, if these Falls be not formed by such outcropping. 



Thus we have in the ascending series — No. 1, The secondary limestone 

 from the first Bluffon the Mississippi, above the mouth of the Ohio, to Cabaue's 

 Bluff on the Missouri, ten or twelve miles below Old Council Bluffs. No. 8, 

 Yellow sandstone (?) to Grand Sioux River. No. 3, Clay stone to lower end 

 of Great Bend. No. 4, Nicollet's clay to a point between Beaver and Grand 

 Rivers. No. 5, The Yellow stone formation. It will be perceived that the loca- 



