IN RELATION TO MINING POLICY. WOODMAN. 175 



tricts sliow no evidence of repeatino- themselves at the proper 

 geological horizons, but are distinct units ; and further, that the y 

 are definitely bounded on all sides. If one goes out from the 

 center of such a dome, he will proceed from a part in which 

 outcrops and underground cross-cuts show a definite alternation 

 of slate and quartzite belts, rather suddenly into a region in 

 w^hich little if any slate is to be found. This is a typical 

 condition. In just the same way, if one could see a sufficiently 

 deep vertical section, he w^ould find that thousands of feet of 

 quartzite, wdth little or no slate, alternate with a few zones in 

 which slate predominates ; and here would be found the bedded 

 leads. The non-appearance of a bedded slate district on the 

 next anticlines transversely north and south of that district, is 

 itself proof of the presence of a very definite bottom to the slate 

 part of each dome. Moreover, it is known that mud sediments 

 are never deposited as enormously thick but closely localized 

 patches ; but that there is roughly a maximum thickness for any 

 given extent, and this is very small in proportion to the original 

 lateral distribution of the deposit. Judging by these conditions 

 in other parts of the world, the downward limit of the pro- 

 ductive part of our domes should not be many thousands of feet 

 below the surface in any case. In one district the author has a 

 feeling, unsupported by other than circumstantial evidence, 

 that this bottom lies practically at the surface for part of 

 that field. Inasmuch, however, as no borings have been 

 made or shafts sunk on the axis of any true dome to even a 

 reasonable depth, all the evidence on this point that can be 

 assembled with a view to helping us in the future, is external 

 and circumstantial. The one established fact is that there will 

 be somewhere a downward limit to the occurrence of new 

 ^saddles, on each dome. 



Thus far our study has been, perhaps, apparently pessi- 

 mistic. It is intended that the paper as a wdiole shall be any- 

 thing but that. It has been necessary to call attention to cer- 

 tain limitations of operations ; and to sundry facts, and the 



