154 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
related, retarded the discovery of the ore deposits, and that to-day renders it impos¬ 
sible to follow the veins over the surface without first stripping off the*soil and loose 
rock or sinking test pits. In the early stages of mining development in the district 
the course of a newly discovered lode was rarely known until underground work had 
well advanced, and consequently few of the claims were laid out along what after¬ 
wards proved to be lines of outcrop. Furthermore, many of the lodes, such as the 
“Captain system” of the Portland mine and the Dorothy vein of the Gold Coin mine, 
apparently do not reach the surface. Under these circumstances, discussion of the 
lode fissures is limited to those whose positions and courses have been determined 
by underground work. 
In a hilly region the lines of outcrop of inclined veins, when plotted on a map, 
are complicated by curvature due to the irregularity of the topographic surface 
In a study of the fissure systems of a district such as that of Cripple Creek, it is 
desirable to eliminate this unessential complexity and to consider the traces of the 
fissures upon one or more horizontal planes. In PI. XII the principal lodes of the 
district are represented with the courses and relative positions that they would 
have if they outcropped on a level plain 9,500 feet above the sea. A few veins, 
known only at considerable distances above or below the 9,500-foot plane, are 
represented by dotted lines, and have the elevation at which they are known nearest 
to 9,500 feet indicated in figures. The diagram shows also the outlines of the main 
volcanic neck and of the Beacon Hill phonolite plug at the surface, data being 
insufficient for fully delineating these features upon the 9,500-foot plane. 
As shown in PI. XII, the productive fissures are most strongly and abundantly 
developed in the volcanic neck. They are not confined to the neck, however, for 
there is a very important group near Victor, partly in granite and partly in the 
volcanic rocks, and there is a prominent group in the granite of Beacon Hill. Pro¬ 
ductive fissures occur also at other points in the granites and gneiss of the pre- 
volcanic plateau. But even when all outlying fissures are considered, the grouping 
of the lodes within a small area, which is that of the volcanic neck plus a sector of 
a narrow concentric zone of the granitic rim, is the most striking fact of distribution 
brought out by the diagram. Within this general group the fissures of Beacon 
Hill constitute a subgroup clustered about the phonolite plug which forms the core 
of the hill. 
Within the volcanic neck the fissures are most abundant and persistent in its 
southern half. They are crowded within the V-shaped or crescentic area wherein, 
as previously shown, the breccia extends to great depth and most clearly fills a part 
of the old volcanic throat. In the very center of the generally productive tract and 
roughly bounded by lines connecting the summits of Globe, Ironclad, Bull, Raven, 
and Gold hills is an area within which few important productive fissures are known. 
This relatively barren ground includes the superficially isolated granite mass of Bull 
and Ironclad hills and the schist mass of Fairview. North of this area, extending 
to Tenderfoot and Carbonate hills, is a part of the district which, while moderately 
productive, exhibits far less Assuring than does the portion stretching from Anaconda 
to Victor and from Victor to Altman. 
It is certain that the district contains many important fissures not shown in 
PI. XII, but that plate probably expresses fairly well the essential facts of lode 
