100 



** But Professor Jackson assimilates it to the agalmatolite, 

 from which it differs, however, very materially by its general 

 aspect, its conduct before the blow-pipe, and its total insolu- 

 bility in sulphuric acid. 



" Anotlicr feature of the Red Pipestone Valley, is the oc- 

 currence of granitic boulders of larger size than any I had 

 previously met. One of them measured about 60 feet in 

 circumference, and was from 10 to 12 feet thick. They are 

 strewed over the valley, in which it is remarkable that there 

 are no pebbles. 



** On the left bank of the Mankato, six miles from its 

 mouth, in a rocky bluff composed of sandstone and lime- 

 stone, are found cavities in which the famed blue or green 

 earth, used by the Sioux as their principal pigment, is 

 ob tamed. 



" As I did in tlic case of the red pipcstone described 

 above, I will state tlie mineralogical characters of the Indian 

 blue earth, or clay. It is massive, somewhat plastic, emits 

 an argillaceous odor wlicn breathed upon ; — color, bluish 

 green; easily scratched with the nail when formed into 

 hardened balls. The acids have no action upon it ; it is 

 infusible before the blow-pipe, but loses its color and becomes 

 brown. This color is due to the peroxide of iron, which it 



