Xxx INTRODUCTION. 
The notable changes in the above table are, first, the almost tenfold 
inerease in production from the year 1887 to 1888, due to the advent of 
the railroads, and to the compromise of the apex side-line suit; second, the 
decrease of nearly one-half from the year 1892 to 1893, due to the sudden 
decline in the price of silver, and in part to the working out of some of the 
large bodies of very rich ore that had increased production greatly during 
the two or three previous years. 
GEOLOGICAL INVESTIGATIONS. 
The mines of Aspen were mostly discovered and opened by men whose 
most recent mining experience had been at Leadville, where the silver ores 
were found principally at or near the contact of limestone with overlying 
sheets of porphyry, and where the great faults, having been formed since 
the period of ore deposition, were barren of original deposits. In this new 
district, therefore, the miners naturally looked for similar conditions, and 
finding ore between the blue and brown limestone at their outcrop, assumed 
that it was a contact deposit between these two beds, and located claims 
accordingly. 
When, in the summer of 1887, while engaged upon the survey of the 
southern Elk Mountains, the writer made a hasty reconnaissance of the 
Aspen mining district and its immediate vicinity, the contact theory was 
still held by a large part of the mining community, and those who did not 
partake in this belief had no very definite theory to offer in its place. 
The writer’s underground observations, which were made in the com- 
pany of upholders of either belief, led him to conclude that the ore had 
been deposited along fault planes and from there outward into the body of 
surrounding limestone, but he saw that only thorough and careful work, 
based on most detailed maps, both of surface and of underground workings, 
could finally determine these questions on a scale of accuracy proportionate 
to the magnitude of the interests involved. He therefore urged upon the 
Director of the Survey the importance of having such a monographic study 
made of the district, but it was not until the summer of 1890 that it was 
found practicable to commence a survey for special topographical maps 
of the region. ‘These maps, made under the direction of Mr. Morris Bien, 
were completed in the summer of 1891, and as soon as printed were dis- 
tributed among those interested in Aspen mines. These persons, who had 
