4 S 0 WISCONSIN STATE AG HI CULTURAL SOCIETY . 
out excavation. Along the river banks, however, we have good exposures, 
and it is here only that w T e can study the structural character of this forma¬ 
tion. 
Along these exposures, especially along the Yellow river, which is 
nearest the centre of this north and south “ anticlinal,” we find this gran¬ 
ite belt traversed with large dikes of partially decomposed, or what is 
sometimes called ‘ rotten rock.’ In these dikes the feldspar shows strongly 
this tendency to decompose into kaolin. In places, it is only partially 
changed, that is, it has a whitish appearance, but retains the crystalline 
structure of the mineral; while in other places it is a soft white powder 
where dry, but where it is damp it has a clayed appearance, although still 
retaining its place in the rock. One of those dikes is found on property 
owned by a Mr. Pitts, is several rods wide, and well exposed. Since I was 
there, and called attention to these things, another place, I am told, is dis¬ 
covered to the west of the river, towards Black River Falls, that is very 
similar. 
On the Wisconsin river, and in the city and neighborhood of Grand 
Rapids, where wells and cellars have been dug, and other excavations made, 
beds of genuine kaolin, or porcelain clay have been found, varying in thick¬ 
ness from one to five feet. Indeed it is very difficult to sink a pit anywhere 
in that neighborhood without finding more or less of this material. And 
when we take into consideration the fact that the same character of rock, 
and the same physical conditions continue from Grand Rapids on the Wis¬ 
consin river, to the Black river on the west, a distance of fifty miles or more, 
we can hardly see how it can be otherwise, than that there should exist 
somewhere along this line extensive deposits of kaolin. The value of 
extensive deposits of this material, in this part of the state, at this time, can 
hardly be estimated, and it is to be hoped that parties in those regions will 
soon wake up to its importance, and develop those already important pros¬ 
pects into a shape that will attract the attention of parties who are anxiously 
looking for such material for manufacturing purposes. To aid this, I will 
here refer briefly to the nature of kaolin, its mode of deposit and uses. 
Kaolin is the native silicate of alumina, and one of the most refractory clays 
found in nature. It will stand the highest temperature, without fusing 
or getting out of shape. It is usually, though not always formed from de¬ 
composed feldspar, and in this respect is one of those alterations in rock and 
mineral formations that often take place along those lines of physical dis¬ 
turbance, or chemical activity in the earth’s crust. Kaolin, however, is not 
simply decomposed feldspar. In the process of decomposition, a chemical 
change takes place, and kaolin is the result. “ Three atoms of feldspar to¬ 
gether,” says Dana, “ consist of three parts of potash, three of alumina, and 
twelve of silica. If three parts of potash, and eight of silica, be removed, 
it leaves three of alumina and four of silica, which is the composition of 
kaolin, except that six of water are added.” 
Kaolin is also a mineral, and is often found forming a part of mineral 
veins, consequently may have some other origin than the one referred to. 
