IN RELATION TO MINING POLICY. AVOODMAN. 171 



feet ; but no lead lias ever been traced out of its district to an- 

 other one, either on the strike of the fold, or transverse to it. 



Not only is this point clear, but another equally important 

 one is proved by the same evidence — namely, the discontinuity 

 of the horizons of slate belts which the veins accompany, and 

 which are invariable characteristics of the domes. All who 

 work the leads of the various districts know that they are not 

 to be found, except in rare cases, away from slate belts ; and 

 " whin bound " leads are generally shunned, This holds true 

 within the districts, — that is, on the known domes, — and equal- 

 ly outside these limits. No prospector wastes his time on 

 country definitely known to be all whin. Now, not only do 

 individual leads and groups of leads fail to " carry " over from 

 one district to the next, but the slate belts in which they are 

 enclosed fail to be continuous, either on the strike of the folds 

 or transverse to it. More than that, the general horizons 

 occupied by the domes, which elsewhere (The sediments of the 

 Meguma series of Nova Scotia. Avier. GeoL, July, 1904 ; vol- 

 xxxiv, pp. IS-SJf., esp. p. 17) the author has called " horizons 

 of most abundant slate," are localized in each and every case, 

 confined to the particular dome on which we find them. This 

 is proved, as in the case of the veins, by structural studies. 



The great importance of recognition of this fact is apparent 

 when it is seen that, according to this, each mining district has 

 a definite limit, not only longitudinally east and west, and 

 transversely north and south, but vertically downward. The 

 deduction has a direct bearing upon the problem of deep mining. 

 To put the matter more plainly, it will be necessary to look for 

 a moment at the origin of the leads and their environing slates. 

 The present distribution of the slate horizons shows that 

 each group of slate belts, each district, is isolated; and that 

 as far as known no two are to be correlated as of exactly 

 the same age. That is, no two were simultaneously and con- 

 tinuously deposited. Between adjacent domes, in all directions 

 the outcrops show prevailingly quartzite or whin. It appears^ 



