20 Wisconsin Academy of Sciences, Arts, and Letters. 
Southwestern Wisconsin and Northern Illinois. —As early as 
1866 Whitney 3 showed that the Galena limestone formation is in¬ 
tersected by two sets of vertical fissures whose directions are ap¬ 
proximately east and west, and north and south. 
“All through the mining district, indeed, in Wisconsin and 
Iowa as w'ell as in Illinois, the heaviest diggings will usually be 
found on crevices varying but little from east to west in their 
general direction. . . The norths and souths on the other 
hand or those crevices which have a course approximating to the 
meridian, are much less important, although these in some in¬ 
stances are the most productive ones of portions of the lead re¬ 
gion.” Buckley as a result of his measurement of joint direc¬ 
tions within the quarries of the State of Wisconsin makes the 
following general statement. 
“As wdll be seen in the accompanying map the joints of the 
sedimentary rocks strike in four main directions. The prevail¬ 
ing general direction of the joints is northeast and southwest. 
The other directions are northwest and southeast, east and west, 
and north and south.’’ 
An examination of Buckley’s map will show that the interme¬ 
diate directions vary in many cases widely from the forty-five 
degree positions. Under the writer’s direction Mr. E. C. Harder 2 
has made a careful study of the joint systems which are devel¬ 
oped in the rocks of southwestern Wisconsin. For this province 
as a w-hole he finds that in order of numerical superiority the 
dominant joint directions of the district are, N. 35° E., N. 75° E., 
N. 35° W., N. 55° W., N. 45° E., N. 85-90° E., N. 25° W., N. 45° 
W., N. 15° W., N. 25° E., N. 65° E., N. 75° W., N. 65° W., and 
N. 55° E. The tendency of the five degree interval to appear 
is noticeable and indicates that here as elsewhere the observa¬ 
tions of slightly curving planes become adjusted to the larger 
unit of the compass. Thus the equatorial direction, which is the 
dominant one, should probably include the measurements rang¬ 
ing between N. 85° W. and N. 85° E., or 25 in all. Only less 
noticeable aggregations appear elsewhere in the table, where 
i Whitney, J. D. Geology of the Lead Region. Geol. Surv. Ills., Yol. 
1, 1866, p. 194. 
2 Jour. Geol. Yol. 13, 1905, pp. 363-366. 
