286 Hawortli on the Archcean Geology of Misso%iri. 
the St. Francois. The quarries along Stout's creek are at the 
water's edge. These are the locaHties in which the hest crys- 
tallized granites occur. As we go back from the streams to- 
wards the hills the surface is usually covered with soil, so that 
the rocks can not be seen. The hills are almost invariably 
composed of porphyry. There is a considerable area of granite 
exposed to the west of Syenite, on both sides of the county 
line between Madison and St. Francois counties. This is on 
the highest ground of any granite exposures observed. In ap- 
pearance these rocks very decidedly resemble the jjorphyries, 
much more so, at least, than do the granites of the valleys. In 
other cases the porphjries seem to be very coarsely crystalline 
for such rocks. At the base of the hill just west of Hogan a 
rock occurs which is difficult to classify. It seems to be half-way 
between a granite and porphyry. Farther south the porphvr 
rytes are so coarsely crystalline they can verv well be worked 
for paving stone. Numerous j^laces along the road south as 
far as Piedmont furnish excellent quarries of such rocks. By 
combining the rocks from these different localities, we have a 
continuous series from the best crvstalline granite of Granite- 
vile, to the most fine grained felsophyre. 
(</). Surface dccoviposi'tlofi. 
Surface decomposition has progressed to a considerable extent 
in some localities. About ten miles west of Pilot Knob there 
are a number of different places in which the porphyry is changed 
to an impure kaolin. At Iron Mountain the surface decom- 
position is very great. When mining was first begun the whole 
surface of the hill was covered with clay through which the iron 
was disseminated. At present quite fresh rocks are exposed 
in some parts of the mine, while in others they are very 
rotten. 
The rocks on the southwest side of Pilot Knob are vei'y badly 
decomposed, as has been shown by borings and diggings. In 
other places similar decomposed areas are met with. Yet one 
is perfectly correct in saying that the great masses of the rocks 
are comparatively fresh. With but few exceptions one can get 
a good, fresh hand specimen by using a hammer on the ledges 
of any hill-side. 
