682 GEOLOGY AND TOPOGRAPHY OF THE LEAD REGION. 



There exists at Mineral Point, at an elevation of about fifty feet 

 above the upper surface of the Baft' limestone, or quarry rock, a ' 

 stratum of compact limestone several feet in thickness, which in color 

 and texture closely resembles the lowest recognized Blue limestone, 

 and contains Strophomena alternate, Leptoena sericea, Bellerophon 

 fiilobatus, and some varieties of Orthis, all in great profusion, and all 

 of them characteristic of the Blue limestone below. The strata 

 which separate them are not exposed. 



It seems probable that this upper stratum may correspond to Xo. 

 5 of the preceding section; that Nos. 6 and 7 are the unexposed beds 

 at Mineral Point; and that Nos. 8 and 9 of the Darlington section 

 represent the Blue and Buff limestones at Mineral Point. The rela- 

 tions of the two principal fossiliferous strata are not, however, fully 

 apparent in the Lead region, nor does the upper one seem to be of 

 constant occurrence, whereas the lower one is universally recognized 

 in Iowa, La Fayette and Grant counties. 



East of range three east, the presence of the Blue limestone is no- 

 where so clearly marked as west of this line. It is usually recog- 

 nized by the outcropping of a quantity of highly fossiliferous frag- 

 ments, scattered through the soil, having a worn and bleached appear- 

 ance. East of range three the fossiliferous Blue limestone was not 

 found. It is replaced by a yellowish limestone, containing but very 

 few fossils, and in all respects similar to the Buff limestone. The 

 thickness between the Galena limestone and St. Peters sandstone 

 remains as usual, about fifty feet. 



There are two exceptions to the foregoing general statement. A 

 short distance south of the center of sec. 18, T. 1, R. 6 E, the Blue 

 limestone reappears in its full thickness, with all its characteristic 

 fossils, but only covers a small area of ground. 



The second exception is situated in the town of Mt. Pleasant, in 

 Green county, in the S. E. qr. of Sec. 11, T. 3, R. 7 E. It is known 

 as the Marble Quarry, so named on account of the fine, polish which 

 may be given to the stone. The Blue limestone has here the same 

 thickness, both of the thin and thick beds, as in the western part of 

 the Lead region. All the characteristic fossils are present, and in 

 short, it presents all the usual lithological appearances. It appears 

 to have been deposited in a basin-shaped depression, as the top of the 

 St. Peters was found to be much lower here than any where in the 

 vicinity. Although separated many miles from any other outcrop of 

 the Blue limestone, it is evident that it w#s deposited under the same 

 conditions, as in other localities. It has been used here for burning 

 lime, of which it always makes a good article. Some small pieces 



