36 LIMONITE AND LIMESTONES—GILPIN. 
and as a substitute for the Limestone, would be gradually oxy- 
dised and hydrated, as the air and water obtained access to it; 
and the same action would also change the beds of Spathie ore. 
The action being continuous, and extending over a long inter- 
val of time, the deposits would gradually assume proportions of 
economic importance, in spite of the large quantities which 
would be removed by the various physical changes the district 
has undergone. Jn places which were not so much broken by 
faults, or where the strata were more compact,’the Spathic ore 
would escape the oxydising prozess and remain to the present 
day as the Carbonate. 
Gradually, as the erosion went on, these deposits would keep 
forming, and be more or less swept away. <A large quantity of 
the ore would naturally rest on the comparatively dense Silurian 
slates and the eglges of the Lower Carboniferous strata. Other 
bodies would become consolidated in the hollows formed in the 
Limestones. The beds of Spathose ore would become oxydised 
more or less generally, and the lines of fracture in the Silurian 
slates would also become receptacles for the ore. 
Although as yet nothing beyond exploratory work has been 
done at these deposits, the sections attainable furnish instances 
of all the above effects, which we weuld theoretically expect. 
The oxydation of the Spathic deposits is shown by a section 
forming the counterpart of the one already referred to. 
In this section we find a gore of argillaceous ochre or clay 
resting on the Silurian slates and replacing the breccia, and the 
Limonite replacing the ferruginous Limestone. 
In another exploration a deposit of the Limonite was met 
under peculiar circumstances, which at first appeared to be dis- 
cordant with the preceding sections and theories. It was, 
apparently, a bed in the Silurian clay slates, but this idea could 
not long be entertained, as it was in a perpendicular position, 
while the neighboring slates had a uniform dip of about 50° and 
cut it obliquely in their strike. The deposit pursued a course 
parallel to that of the valley, and the enclosing slates were much 
fissured and filled with veins of Limonite and Calespar. 
It appeared to me that this was a fault which had perhaps for- 
