470 



GEOLOGY OF EASTERN WISCONSIN. 



Fig. 5. 



of carbonic acid remains as an indicator of the mode of decomposition which has led to 

 the formation of the kaolin. 822 B is the fine portion of the same clay separated by 

 levigation in the laboratory from the admixture of coarse sand composed of quartz and 

 undecomposed felspar fragments, the former predominating. The smaller percentage 

 of alkalies is due to the removal of the felspar fragments and mica flakes. 823 A and 

 823 B are raw and washed clay from the next exposure above, along the stream. A les- 

 sening of the alkali percentage is again to be observed in the washed clay. 823 repre- 

 sents an apparent thickness of nearly three feet. 824 is from the exposure furthest up 

 stream. It is quite soft and clayey, but in places retains the rock lamination to a 

 marked degree. 824 A and 824 B are respectively the raw and levigated clay. It will 

 be noticed, that, although retaining the rock structure, this clay is yet pretty completely 

 decomposed, the only point indicating a lack of thorough decomposition being the larger 

 amount than usual of soda. 825 is a still firm, partly decomposed rock from the same 

 place as 824. It is of a dirty white color on the exterior, nearly pure white on the inte- 

 rior, quite porous, has an evident gneissoid texture, and is speckled with small flakes of 

 silvery mica. With the exception of this mica no distinct constituent minerals can be 

 seen with the naked eye; with a magnifying glass, however, a fresh fracture reveals in 

 a few places minute grains of quartz and undecomposed orthoclase felspar. The large 

 tenure of alkalies, especially of soda, and the small amount of water, indicate the only 

 partial decomposition. 



Appearances would indicate the existence of a considerable body of kaolin at this 

 point. Since my examination the locality has been much further developed and a large 

 number of fire brick made. In 1875, Mr. E. T. Sweet, of the Geological Survey, vis- 

 ited the place and found that no care was taken to select the clay, nor was it put 



through any washing process to separate the unde- 

 composed portions. He was informed that woodash 

 was used largely to counteract the shrinking of the 

 clay on burning; an addition, which, of course, in- 

 troduced the ingredient most to be dreaded. As a 

 result of this method of manufacture and lack of se- 

 lection, a very great variation was observable in the 

 quality of the bricks, some even showing a tendency 

 to agglomerate in the kiln. The clay from this local- 

 ity has also been largely shipped raw to Milwaukee 

 where it has been used by the Iron Companies and 

 Gas Light Company. In 1874, about one thousand 

 brick were burned for the Gas Light Company from a 

 mixture of the Grand Rapids kaolin and pulverized 

 fire-brick, and were found to be of the very best qual- 

 ity. 1 A brick made in this way, and procured for me 

 by Mr. S. G. Lapham, yielded 2.06 of potash and 

 0.31 of soda. It presented a peculiar jagged, porous 

 appearance on a fracture, with blotches of a white 

 porcelain -like substance, and was said to be an excel- 

 lent brick. At the Bayview Iron Works 2 the clay 

 has been tried raw, and found very refractory. 



Bricks made from it and used here were found to vary very much in their refractoriness, 

 some being extraordinarily refractory, others succumbing readily to the heat. 



On Mr. H. Canning's land on the west half of the N. E. qr. of Sec. 26, T. 22, R. 5 

 E., several pits and a well have been sunk into decomposing rock and kaolin. Speci- 

 mens from here yielded the following analytical results : 

 Letter from Dr. I. A. Lapham, Milwaukee, Nov. 13, 1874. " Letter from Mr. J. J. Hagerman. 



VICINITY OF GRAND RAPIDS, 



WOOD COUNTY. 

 Scale, one mile to the inch. 



