SURFACE GEOLOGY. 665 



The turf is underlaid by an impervious stratum of blue clay, which 

 holds the water and nourishes a vegetable growth about four feet 

 thick, which, in this section of the country, is known as peat. AV^hen 

 cut and dried, it burns similarly to peat, but with so large a residuum 

 of clay, sand and ashes, as to render it unfit for economic purposes. 



Brick Clay. Clay suitable for making brick is found in many 

 parts of the Lead region. Among the localities are Lancaster, Min- 

 eral Point and Platteville. The first has two yards in operation, and 

 the latter has one, which commenced operations in the spring of 1874. 

 The clay used is usually of a grayish-yellow color which becomes red 

 on burning. It appears to have been formed in the same manner as 

 other portions of the soil, as already described. 



In the Platteville yard an opportunity was found to see the process 

 of manufacture. The clay is dug from an adjacent bank, some selec- 

 tion being necessary. It is then run on small cars to the pug-mills 

 (which are three in number) and ground with water, until it forms a 

 homogeneous paste. After this comes the moulding into bricks, 

 which are spread out on the floor of the yard, dried and piled in a 

 kiln to burn. A kiln of these bricks takes about eight days to burn. 

 It is estimated that about 8,000 bricks per day can be made in this 

 yard. 



In the city of Monroe, in Green county, is a brick yard where two 

 kinds of brick are made from the same kind of clay. One is a red 

 brick, similar to all common red brick; the other is a cream-colored 

 brick, of very handsome appearance, closely resembling the Milwaukee 

 brick. From the lalter, many of the handsomest buildings in Monroe 

 are constructed. The difference in color is due to the difference in 

 burning, the red color being caused by a greater and long continued 

 heat. 



The origin of the clay of which the brick are made is a matter of 

 some doubt. It does not have exactly the appearance of a drift clay ; 

 and if not, its situation indicates that it must have undergone some 

 subsequent rearrangement. 



Glacial Drift. As has been before intimated, the Lead region is 

 a driftless tract of country; not a single bowlder, pebble or clay of 

 foreign origin being found in its limits, except in three or four 

 isolated cases, which will be hereafter described. 



The northern boundary line of the driftless region lies far to the 

 north of the Lead region. The eastern line was found in Green 

 county, and traced out with all possible accuracy. For a particular 

 description of it, reference is made to the geological maps; in brief, 

 however, it is as follows: It commences on the west side of the Pec- 



