2 So Haworth on the Archcean Geology of Missouri. 
I have chemically examined them, a larger per cent, of iron, and are 
coarser in texture. 
It is but justice to Prof, Aughey that his account of this de- 
posit should be accredited for all it is worth; and it may be the 
means of correcting an error. I do not assert that the opinion 
which seems now to be widely entertained is erroneous. I wish 
to provoke further investigation. 
The relation of the silico-alkaline earth to one of the extinct 
geyser tubes was recently observed in the Loup region by Mr. 
F. W. Russell. He also reports a warm spring in that region. 
The condition of fine powder which the mineral in question 
usually presents is not a serious objection to its being regarded 
as geyserite. The explanation may be such as Prof. Aughey 
suggests; besides ordinary geyserite often falls to powder on 
exposure. The specimens which I have seen from Nebraska 
were all in fine powder, but Prof. H. H. Nicholson of this Uni- 
versity assures me that it does occur here in the form of solid 
incrustations as in existing ge3^ser regions. The specimen from 
Kansas has greater solidity than any I have seen from Nebraska^ 
but it is quite friable. 
A CONTRIBUTION TO THE ARCH^AN GEOLOGY OF 
MISSOURI. 
WITH PLATE I. 
BY ERASMUS HAWORTH. 
CONTENTS. 
1. Gkneral Considerations. 
A . Geography. 
B. Statement of ivork. 
C. General Geology, {a) General geological characters, (h) 
Relation of stratified to massive rocks, (c) Relation of massive 
rocks to each other, (d) Surface decomposition, (e) Dykes. 
II. Petrography. 
A. Granites, (a) Mineralogical composition. (Z*) Special de- 
scription of minerals, (r) Structure of the granites. (J) Classi- 
fication of granites. 
B. Porfhyries and Porfhyrytes, exclusive of dyke rocks. («) 
Mineralogical composition, (h) Special description of minerals. 
