Mineral Deposits of Southwest Wisconsin. — Blake. 241 
o'clocks," or having a direction nearly N. 20° to 30° W. This 
general parallelism of the ore-bearing groups with the struc- 
ture of the region is significant of some relationship or de- 
pendence which has not hitherto been fully investigated. 
Percival gave great attention in detail to the direction of the 
crevices, and generally refers to them as "norths and souths" 
and " easts and wests," while recognizing the general bearing 
as quartering or northeasterly and southwesterly — his east 
and west ranges being in fact the same as those approximat- 
ing a northeasterly and southwesterly course. He says : "The 
term east and west is applied to the leading ranges, although 
they may deviate even 45° from a due east and west course."* 
He also pointed out the fact that the traces of order and con- 
nection in the surface arrangement appear no less remarkable 
than in the vertical arrangement, and that the ore-bearing 
ranges in their bearing (direction) and grouping have been 
governed by some general laws, and have not been merely 
local accidents. f 
Horizon of Ore-Deposits. 
The question whether the ores of lead and zinc are confined 
merely to the horizon of the Galena limestone and to the up- 
per portions of the Trenton or extend much lower, even into 
the Lower Magnesian limestone, has been much discussed by 
the successive geologists of Wisconsin since the days of Per- 
cival, who favored the view of the deep-seated source of the 
ores and their presence in the lower formations. This view 
was emphatically discouraged by Whitney and by Chamber- 
lin, whose conclusions have been generally accepted, and no 
effort has been made to test the question practically by a 
deep shaft, as has been several times proposed. 
Chief Deposits of Beende. 
The bulk of the blende comes from bedded or horizontally 
distributed ore and not from vertical or inclined crevices. 
The deposits show less irregularity of formation than those 
of galenite, being for the most part below the general water 
level, and not affected by oxidation and the attendant solu- 
tion of the rocky walls and the formation of irregular caverns. 
* Report of 1855, p. 76. 
t PercivaPs Report of 1856 (second report, published after his death), 
page 63. 
