71 [ 237 ] 



•according to the division adopted by Doctors Locke and Owen, in their 

 report of the Galena group. 



Mr. Featherstonhangh has corrected an error into whic'n Mr. Keating 

 had been led, by mistaking the fallen masses of the uppermost stratum 

 of limestone in the bed of the river at St. Peter's for underlying rocks in 

 place. These fragmentary rocks were there, in fact, when Mr. Keating 

 visited the spot, of which I have satisfied myself; but they have since' 

 disappeared, and, at all events, were not there in July, 1836. They were; 

 most probably removed, partly by attrition, and the dissolving properties' 

 of the waters of tlie river, which are highly charged with carbonic acid. 

 A weathering of this sort is accordingly observed on both sides of the 

 Mississippi, on a distance of eight miles, from St. Peter's to the Falls of 

 St. Anthony ; at which latter spot it takes place to a greater extent. The" 

 underlying sandstone, being very friable, is easily acted on by meteoric and'^ 

 atmospheric agencies. The first effect of these is to form excavations in^ 

 the sandstone, which, crum.bling in, carries along the superincumbent' 

 limestone thus deprived of its support. 



In ascending the Mississippi in this last-mentioned distance, the trav- 

 eller is astonished to find its bed so little encumbered by the debris of 

 Ihis limestone ; and at the St. Anthony, he is still more surprised not to- 

 find a larger accumulation of detritus at the foot of its falls. This is" 

 owing to the solvent properties of the water previously alluded to; so* 

 that I have not the least doubt that the limestone at one time covered arii-' 

 exteuvsive tract of country, and that the waters reaching the sandstone;! 

 the result of this species of denudation has brought about the peculiar ' 

 configuration of the surface in this region of country, as seen on the 

 left bank of the Mississippi, going from the St. Peter's to Carver's cave, 

 and over the whole district watered by La Hontan and Vermillion river?,' 

 and other places. These causes of erosion are doubtless still in fullac-' 

 tivity, and hence I am inclined to think that the recession of the Falls of' 

 St. Anthony is much more rapid than is generally supposed. As it is 

 possible to find elements for the measurement of this result, 1 made sur- 

 veys of the locality in the month of March, 1839. I have appended to 

 this report a chart of the falls, exhibiting diagrams of their dimensions at 

 that time, which will enable future generations to calculate the progress 

 of their annual recession. The limit of the geological formation of St. 

 Peter's is a mile above the falls, at the creek to which I have assigned 

 the name of Falls creek on my m;ip. When the falls shall have reached 

 this spot, it is probable they will come in contact with crystalline rocks 

 forming the bed of the Mississippi, and consequently the recession will be 

 infinitely slower. 



As it is important, in geology, to determine the precise limits of forma- 

 tions, I shall add a few words on this subject. The geological formation 

 of St. Peter's continues to show itself in the river of the same name, and 

 goes on thinning out as far as Waraju river, (the riviere aux Liards oi 

 the French.) and there it disappears. Hence it passes to the headwaters 

 o{ Mankato river, crosses the southern part of the Ceteau des Prairies^ and 

 finally loses itself in the Missouri, Sioux, and Iowa rivers, as previously 

 explained when describing the extent of the cretaceous formation. To 

 the east, starting from St. Anthony's Fails, it may conjectu rally be staled 

 to cross the St. Croix, make its appearance on Manomin, Chippeway, and 

 Sapak rivers, not far from the rapids and falls of these rivers, and thea 



