360 The American Geologist. June, 1901. 
profoundly eroded as to expose all formations down to the 
Cambrian ; while in the south, in Arkansas, where sedimentation 
went on uninterruptedly, strata to a thickness of 20,000 feet ac- 
cumulated. Along the horizon of this peneplain there is no 
evidence of notable deposits of ores of any kind. 
Beds belonging to the upper part of the Coal Measures 
are now known to occur on the highest parts of the present 
Ozark dome. Small doubt therefore exists as to the extension 
of the Coal Measures (Des Moines and Missouri series) en- 
tirely over the region occupied by the great uplift. This is 
also, according to our best knowledge on the subject, probably 
true of the Cretaceous strata. Before, however, the deposits 
of the latter were formed another long period of erosion inter- 
vened. Yet in the known remnants of the peneplain which 
was formed at that time no signs of the existence of ore bodies 
are found. 
Again, when the Ozark region was bowed up and planed 
oil in Tertiary time down to the pre-Cambrian basement, no 
indications are presented that the peneplain which is the pres- 
ent general upland surface of the dome, is a horizon that is a 
special ore-bearing level. As already stated, it is in the central 
part where degradation has been greatest that ore deposition 
has been least. 
We are forced to the conclusion, at least so far as the 
Ozark region is concerned, that degradation and surface de- 
composition even though so profound as to remove thousands 
of feet of rock, do not tend to concentrate whatever diffused 
metallic content the strata may contain. While profound sur- 
face decomposition is an important factor in the formation of 
ore deposits, bv itself it produces no effect in this direction. 
There must also be special geological structures and special 
geological conditions always present before the localization of 
ore material is possible. 
Without attempting to discuss or furnish detailed evidence 
at this time, it may be in this connection granted that most 
rocks actually do at all time contain in a dift'used condition 
ample supplies of most common metals to furnish materials for 
the richest of ore deposits, that subterranean waters are con- 
stantly transferring laterally from one point to another metallic 
substances along with many others which are not ore-forming. 
