GEOLOGICAL FORMATIONS. 



683 



have been polished for paper weights, and other small ornaments. It 

 takes a high polish, equal to marble, although large pieces cannot be 

 obtained. 



One other bed has been observed, not mentioned in the descriptive 

 section. It is the line of demarkation between the Buff limestone 

 and St. Peters sandstone. It consists of a greenish blue clay, usually 

 from one to two feet thick. The clay is very finely laminated, and 

 consists of argillaceous and calcareous matter. It might be valuable 

 as a marl, were there not so much of the same constituent parts in 

 the surrounding soil, as to make its application superfluous. It is 

 not a bed of invariable occurrence, but it has been seen in so many 

 localities, over a great extent of country, that it may be regarded as a 

 constituent bed of the formation. 



Ores and Minerals. The Blue and Buff limestones are the low- 

 est in which any ores are found in sufficient quantities to repay min- 

 ing, and the northern and eastern parts of the region in the vicinity 

 of Mineral Point, Linden. Dodgeville, Highland, Centerville, Mifflin, 

 and the Crow Branch Diggings are the most remunerative. It is not 

 to be inferred from this that the formation is barren in the southern 

 and western parts, but rather that it lies so deep that it has not yet 

 been reached in the present system of mining. 



Large bodies of lead ore have from time to time been taken from 

 this formation, but it seems to be more especially productive of zinc, 

 both as carbonate and sulphuret. At present the zinc furnished from 

 the localities above mentioned is chiefly derived from it. For statis- 

 tics of this product, the reader is referred to the latter part of this 

 report, chapter IV. 



Organic remains are found in the greatest profusion, and in a very 

 fine state of preservation, the rock in many places being entirely com- 

 posed of them. In the Buff limestone the} 7 usually occur as casts. 

 Without particularizing, reference is made to the general list. 



GALENA LIMESTONE. 



Geographical Boundaries. This formation is by far the most im- 

 portant in respect to its metallic wealth of all which we have to con- 

 sider. In it are contained all the mines of the southern and western 

 parts of the Lead region, and whenever mining has been carried on 

 in the underlying Trenton limestones, lead is usually present in the 

 overlying Galena. 



1 In describing this formation the term " Galena limestone," used in other reports, has 

 been adhered to in this, to prevent the confusion arising from several names for the same 

 thing, although strictly speaking it is a dolomite. 



