170 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
nearly so. This is indicated by brecciation between the blue limestone 
and the dolomite. Second, the mineralization and deposition of vein 
material. This is shown by the fact that the breccia along this fault has 
been changed to ore, and has in large part been cemented by vein mate- 
rial, chiefly barite. The mineralization, therefore, is later than the faulting. 
Third, dolomization. This was probably contemporaneous with the min- 
eralization, but may have gone on somewhat later. It is indicated by the 
alteration of the blue limestone in the immediate vicinity of the Contact 
fault to dolomite. The irregular distribution of this dolomite, following 
fractured zones and occurring in nonpersistent bands and blotches, shows 
that it could not have been originally deposited, but that its deposition 
came about through the waters which circulated through the fault zone. 
Fourth, a movement of the rocks at a later period and a widening cf the 
original fissure. This must have left an open fissure of varying width. 
The opening of this fissure subsequent to the ore deposition is shown by 
the fragments of ore as well as of limestone and dolomite in the clay which 
subsequently filled it. Fifth, the deposition of bog manganese during a 
period when the waters which filled the opening were comparatively quiet. 
Sixth, a slight tilting of the rocks, which is shown by a gentle dip in the 
mud layers and by some disturbance in the manganiferous lower layer, 
which is often broken. Seventh, the deposition by a more rapid and 
muddy current of the sandy and limy layers. 
At the southern end of the mine a fault is encountered which may be 
the Dixon. This cuts off the Contact fault and the ore, and although there 
is blue limestone on both sides, showing that the throw has not been great, 
the other side has not yet been sufficiently explored to show the exact 
amount of displacement. 
Bob Ingersoll mine—T he Bob Ingersoll mine immediately adjoins the Best 
Friend to the east, the workings of the two mines running together. The 
general occurrence of the ore and its nature are exactly the same as m 
the Best Friend. From the Bob Ingersoll an incline runs down on the 
Contact fault to the north and encounters the Hallet fault, which runs into 
it at the end of the incline. This shaft is 210 feet deep, and has passed 
through porphyry and Weber shales to the Silver fault, at the contact of 
shales and blue limestone. This contact is brought down by the Hallet 
fault to about the level of the Contact fault at the end of the incline. At 
