662 GEOLOGY AND TOPOGRAPHY OF THE LEAD REGION. 



line. One group is near the former residence of Ebenezer Brigham, 

 at the foot of the East Blue Mound, in the S. W. qr. of Sec. 5, T. 6, 

 R. 6 E. There are about a dozen of them, nearly round, varying in 

 diameter from ten to twenty feet, and about five feet deep, all in a 

 line, bearing about 10 north of west. At the West Blue Mound 

 there are several lines of them, about the base and side of the rnound. 

 On the center line of Sec. 1, T. 6, R. 5 E. there is a well defined line 

 of them, extending for about a quarter of a mile on each side of the 

 center of the section. There is another range of them near the 

 center of the S. W. qr. of Sec. 1, and a third line near the quarter 

 post of Sees. 1 and 12. The largest of these sinks is an isolated one 

 near the center of the S. E. qr. of Sec. 1, which is as much as fifty 

 feet in diameter, and twenty feet deep. In this one the wall rock of 

 the fissure could be very plainly seen on the south side. From tho 

 circumstance of their direction and position coinciding with that of 

 all the mineral crevices in the vicinity, and the fact that the ore is 

 always found in large crevice openings, the inference seems to be that 

 these sinks mark the line of large open crevices in the rock beneath 

 them. It is also reasonable to suppose that the sinks along the cen- 

 ter line of Sec. 1, T. 6, R. 5 E. are a continuation of those near the 

 Brigham place, as they seem to point almost directly to one another. 

 It is probable that the water, percolating through the earth into these 

 crevices, has in process of time carried so much of the soil with it 

 as to cause a falling in of the surface, leaving the sinks as the result. 

 In view of the vast quantity of ore which has in former times been 

 obtained from the crevice openings in this locality, it would seem to 

 be worth while to prospect some of these sinks; but nothing of the 

 kind has ever been done. 



Sinks do not appear to be confined to the Galena limestone, but 

 seem to be quite as frequent at the Blue Mounds in the Niagara 

 formation. They have been observed in many other localities in tho 

 Lead region. The following are cited, to show their occurrence in 

 the several formations. On the S. E. qr. of Sec. 14, T. 5, R. 2 W., 

 are three, situated in a triangular form, in the St. Peters sandstone. 

 This is somewhat exceptional, as the sink holes are usually confined 

 to the limestone formations. On the S. hf. of Sec. 11, T. 6, R. 4 E., 

 are several of these sink holes, from eight to twelve feet deep. 



The largest one noticed is situated on the summit of the ridge, on 

 the S. E. qr. of Sec. 29, T. 6, R. 2 E. It lies in the Galena limestone, 

 and is about 200 feet long, by 100 wide, and about twenty feet deep. 



