154 CLASSIFICATION OF THE PUBLIC LANDS. 



Prospects amd mines. — An important part of the examining geolo- 

 gist's work is to note the location of all prospects and mines and to 

 examine all of them, with the possible exception of those that are 

 well known as producers. The most obviously useful data to be ob- 

 tained from mining properties concern the value and visible quantity 

 of the ore and the production if the property is producing. The 

 examiner checks one against another his own observations, the infor- 

 mation given by assay certificates and smelter returns, and the tes- 

 timony of owners or mine officials, which may be in the form of an 

 affidavit if it is thought desirable by an examiner who is empowered 

 to administer an oath. 



The information gathered from a prospect or mine may do much 

 more than indicate the mineral or nonmineral character of the claim 

 on which it is located and that of a little land in its immediate 

 vicinity. The most useful clues may be obtained in openings which 

 permit comparison between the appearance of a lode underground 

 and that of its outcrop. By making these comparisons the examiner 

 is much aided in recognizing the outcrops of important lodes that 

 have not been opened, and by study of the geologic environment of 

 prospected deposits he may form an opinion as to where others are 

 most likely to be found. 



Samples and assays. — Ore samples and assays showing their value 

 give the most concrete evidence and have great weight at public hear- 

 ings. To obtain abundant samples and assays, therefore, is one of 

 the examiner's chief duties, and quantity of material is not more 

 important than full information indicating its value as evidence. 

 Samples collected by biased persons axe taken only too often either 

 from the best part of a lode or from the worst part, or even from 

 the wall rocks; and the procuring of truly representative samples 

 requires both judgment and honesty on the part of the examiner. 

 Full records regarding the collection of the samples are indispens- 

 able. Even after every precaution is taken in the matter of collect- 

 ing and record there may be much room for inference, for the weath- 

 ered, superficial portion of a lode, which alone may be accessible, is 

 sure to differ in tenor from the unweathered portion from which the 

 valuable metals are partly or chiefly to be won. Where ores of the 

 base metals are concerned, values may sometimes be estimated by 

 inspection closely enough to dispense with assays. Usually, how- 

 ever, and especially if values in gold and silver are to be found, the 

 classification of any large tract calls for many assays, and material 

 to be assayed for precious metals must be collected with special pre- 

 cautions. Each sample must be large enough to suffice for several 

 assays, so that any result whose accuracy is doubted may be checked, 

 and the material must be broken up and well mixed to insure its 

 homogeneity before it is divided into portions. 



