60 Sioux City Academy of Science and Letters. 
the upper part, the sediment becomes coarser and more 
sandy with frequent layers of soft sandstone. It is evi- 
dent that this deposit was thrown down on a rather rap- 
idly rising sea bottom. 
In the lower layers of fine-grained clay are many 
limpid crystals of gypsum or sulphate of lime. These are 
disseminated through the most dense parts of the clay 
deposits, and it is probable that the disintegration of the 
iron pyrites is responsible for the presence of these crys- 
tals of sulphate of lime. On the breaking up of the iron 
pyrites there would be set free the combined sulphur, 
which amounts to nearly 54 per cent. of the pyrites, in 
the form of sulphuric acid or sulphur dioxide. Some of 
this acid would unite with the lime, which is present 
in small quantities, forming sulphate of lime. 
On consulting with Prof. Alfred N. Cook, chemist of 
Morningside College in Sioux City, he agreed with me in 
the belief that I had found the true causes for the 
“Smoking Bluffs” of the Missouri River region. He gave 
me the following: 
“TJ think the following equations will accurately 
represent the oxydation of iron pyrites: 
2FeS,+90,—Fe [SO,],+3S0,. 
“Some of the SO, would escape and give the odor of 
burning sulphur. Some would dissolve in the water and 
form sulphurous acid, according to the equation, SO,-+- 
H,O—H.SO,.” 
“This would then take on more oxygen from the dis- 
solved air in the water and become sulphuric acid thus, 
H,SO,+ O0—H.SO,.” 
“This would probably account for the presence of 
free sulphuric acid in the rocks that has been noticed in 
some localities near Sioux City.” 
