KAOLIJf IlSr WISCONSIN". 9 



T. S. Hunt* regards as liavins: been the origin of some of tlie bog- 

 ore deposits in the vicinity of the disintegrating gneissic rocks of 

 the Southern States. I allude to this here since it is a fact that 

 bog-ores of considerable value occurs in the Wisconsin kaolin dis- 

 trict and may be supposed to have had a similar origin. 



In as much as the decomposition of the felspar in such a process 

 is hardly ever so completely carried out as to leave none of it un- 

 altered, it results that the kaolins used in the arts show either in 

 their crude or washed state almost always a certain amount of al- 

 kali on analysis. This alkali may be present partly as entirely un- 

 decomposed felspar fragments, in which state it can be completely 

 removed by levigation, and partly as felspar in different degrees of 

 change. All of the latter cannot be separated. 



Many of the best kaolins aspear to have resulted from the decom- 

 position of a rock consisting chiefly of felspar A\ith as small admix- 

 ture of quartz and no mica, known as pegjiiatite.j These, from their 

 great richness in felspar, tend to produced an especially pure kao- 

 lin. The ordinary gneisses and granites on the other hand, by their 

 decay yield a very coarse sandy clay, which may be quite impure 

 from foreign admixtures, or if free from any hurtful impurity, so 

 largely mingled with quartz, as to be very lean in pure kaolinite. 

 In some regions it is noticed that those granitic or gneissic la5'ers 

 more largely composed of felspar than the adjoining beds, tend to 

 alter whilst the rest stand firm. Since these alternating beds are al- 

 ways inclined at high angles, their outcropping edges strike across 

 the country in groups of narrow parallel bands. Thus it comes 

 that kaolin is sometimes found following long straight lines, hav- 

 ing a constant bearing. This fact may be made use of in " prospect- 

 ing " for kaolin. 



Examples of the occurrence of JcaoVuiized rock. — Most of the 

 authorities that I have been able to consult agree in describing the 

 Chinese kaolin, used many centuries before porcelain-making was 

 introduced into Europe, as a result of the disintegration of a grani- 

 toid rock, though 1 have not seen any detailed account. A recent 

 paper| by Baron Von Richthrofen, as already said, gives a different 

 account of the nature of the Chinese article. He says: " I visited 



* * * "^^ the famous King-te-chin, where the Chinese have 

 made nearly all their porcelain for almost three thousand years. I 



* Loc. cit. t Von Cotta's Litliology p. 206, Englisli Ed. % Am. Jour. Sci., cit. 



