METALLIPEEOUS MINERAL LANDS. 153 



channel or in a glaciated area has presumably come to its place by hill 

 creep, and its source should be looked for, after the method of pros- 

 pectors, by following it straight uphill. Normally the parent lode 

 will be found somewhere between-the point where the float was dis- 

 covered and the top of the slope. If a search is impracticable the 

 probable source may perhaps be inferred, on the same principle, 

 within narrow limits, especially if a good topographic map is avail- 

 able ; the source may thus be assigned to a particular section or even 

 to a smaller subdivision. Moreover, the probable source can often be 

 judged within narrower limits than those set by the distance from 

 the point of discovery and the top of the slope. The small fragments 

 of vein quartz, mingled with soil, which may be found almost any- 

 where in a region of deformed rocks, are likely to have crept down- 

 hill for a long distance; but large blocks of quartz thickly strewn 

 over a small and fairly well defined area, especially an elongated 

 area on a moderate slope, may reasonably be presumed to have come 

 but a short distance from a vein. It is evidently necessary, then, to 

 note fully, on the spot, the size and character of the float fragments 

 as a help in judging the source; and their size may also roughly indi- 

 cate the thickness of the parent lode. 



2. Rounded fragments or bowlders of float, especially if in a stream 

 channel in an unglaciated area, may be presumed to have been trans- 

 ported by water. Float of this character is also frequently followed 

 by prospectors up the streams and slopes to its source. This process is 

 too slow and difficult to be employed often by the examiner. But 

 stream-transported float may ordinarily be assumed to have origi- 

 nated in the drainage basin where it is found, and scrutiny of the 

 stream gravels may tell the examiner what to look for in a particular 

 basin. 



3. Float that has been transported by glaciers is subject, to much 

 the same conditions as water-transported float. It is usually to be 

 recognized by its association with moraines and glacial sculpture but 

 may sometimes be confused with float of the other two kinds. It is 

 less feasible to find its source by systematic tracing than to find that 

 of other float, but where the glaciation is local the parent ledge is 

 likely to be near by and well exposed. 



As placer deposits are really one form of float in the broadest sense, 

 this may be the appropriate place to point out their value as indi- 

 cating the auriferous character of the country rock of the drainage 

 basin in which they are found. 



It may be remarked, finally, that exceptionally, owing to migration 

 of divides or their transgression by glaciers, float is found outside of 

 the drainage basin in which it originated. This is most likely to be 

 true of old stream gravels. 



