72 GEOLOGY AND MINING INDUSTRY OF LEADVILLB. 



beds is cut through, the stratification lines are easily recognizable and serve 

 to distinguish this formation from the latter. 



Along the immediate shore-line as, for instance, under the Wash of 

 Fryer and Carbonate hills the upper portion of the Lake beds consists fre- 

 quently of large angular fragments, a number of which are derived from 

 the actual outcrops of ore bodies. 



Recent or Post-Giaciai (r). Theoretically this rubric includes all the beds 

 of the Post-Glacial Quaternary formations, of which there have been recog- 

 nized 5 a the region under survey several subdivisions, namely: the glacial 

 moraines, a sort of bowlder clay or rearranged moraine material which is 

 prevalent in the immediate vicinity of Leadville, where it received the local 

 name of " Wash ; " a sort of terrace formation found in the larger valleys; and 

 the actual alluvial stream bottoms. 



The time allotted to the work did not admit of a sufficiently complete 

 study of these different subdivisions to justify their distinction by separate 

 colors on the map. In practice, therefore, on the surface maps only the 

 alluvial bottoms and the broader accumulations of the terrace gravel in the 

 larger valleys and plains, which are sufficient to completely obscure the 

 subjacent geology, have been indicated. In the cross-sections of the spe- 

 cial map of Leadville, however, where the explorations of shafts have given 

 unusually complete data, the Wash is also included under this rubric. On 

 the surface maps of Leadville and of the various groups of mines both 

 these formations have been left out, as they would have hidden an impor- 

 tant part of the geological outlines of the actual rock surface; they have, 

 however, been indicated to scale in the cross-sections. 



DISTRIBUTION OF SEDIMENTARY FORMATIONS. 



The superficial distribution of the various sedimentary formations, or 

 the relative area covered by their outcrops, being a function of or depend- 

 ent upon erosion, is intimately connected with the existing topographical 

 structure of the region. Were erosion the only factor to be considered, the 

 Archean rocks would be found exposed continuously on the west side of a 

 line approximately representing the old shore-line and in the deeper drain- 

 age valleys and anticlinal axes of the eastern side. The displacements of 



