152 CLASSIFICATION OP THE PUBLIC LANDS. 



compounds of the valuable metals. This is especially likely to be 

 true of copper deposits, whose upper portions are commonly trans- 

 formed to rusty porous masses containing quartz, iron oxide, and 

 other substances that resist the action of the weather. This material, 

 which is known as iron capping or gossan, may contain small 

 amounts of the bright blue and green copper carbonates, but on the 

 other hand it may be wholly devoid of copper minerals. Many lodes 

 that weather to a gossan and others that are composed largely of 

 easily weathered minerals do not project above" the surface and are 

 therefore likely to be overlooked. If a lode is about as hard as the 

 country rock its outcrop is nearly level with the general surface, and 

 the position of a lode composed of soft, easily weathered material may 

 be marked by a trench instead of a ridge. Many veins, again, have 

 no outcrop ; they are covered with soil, and their position is indicated 

 only by float. It is therefore evident that both careful observation 

 and intelligent inference are required to find the lodes and judge 

 whether or not they are likely to prove valuable. 



The proximity of lodes containing minerals in sufficient concentra- 

 tion to be commercially valuable may be indicated by the presence of 

 such minerals or of gangue minerals associated with them, dissemi- 

 nated through the country rock or in the form of narrow stringers. 

 Some minerals commonly so found are calcite, pyrite, siderite, and 

 chalcopyrite. The more easily weathered minerals are likely to be 

 represented by their oxidation products. Siderite, for example, is 

 usually and pyrite commonly represented by pseudomorphs of hy- 

 drated ferric oxide. Extensive rusty staining of the country rock 

 therefore causes the examiner to look for more specific evidence of 

 mineralization. Other characteristic alterations of the country rock, 

 such as leaching, chloritization, and sericitization, commonly occur 

 along the walls of lodes and are therefore useful as clues. 



Probably the great majority of prospectors' discoveries are made 

 by following float ^ to its source, and mineral classification likewise 

 may rest in large measure upon the evidence afforded by float. Time 

 will not always permit the tracing of float to its source, and the ex- 

 aminer must then be content with inferences drawn from the char- 

 acter and situation of the float as he finds it. In any case the first 

 step is to consider how the float probably reached its actual position. 

 It may have done so by either (1) hill creep, (2) water transporta- 

 tion, or (3) ice transportation, or by a combination of any of these 

 agencies. 



1. Most float has been transported to its present position by hill 

 creep, which is constantly active on every slope. Angular float, without 

 marks of attrition, which does not lie in an actual or former stream 



• This term ie commonly applied by prospectors to all fragments of lode matter not 

 In place, however transported ; It will be used In this sense here. 



