KAOLIlvr lis" WISCONSIK". 7 



oxydation of the sulpliid, but is rather due chiefly to the disintegra- 

 tion of the rock produced by this oxydation, which leaves it more 

 easily permeable to the carbonated waters. 



The felspars vfhich appear especially to haye given rise to kao- 

 lin masses are orthoclase and albite, the potash and soda felspars. 

 This must be attributed rather to their greater abundance as com- 

 pared with oligoclase and andesite — the soda-lime felspars — since 

 these latter change much more easily to kaolin, whilst orthoclase 

 changes with the least readiness of any of the felspars, being found 

 often unaltered, when oligoclase occurring in the same rock is com- 

 pletely kaolinized.* Labradorite does not commonl}' alter to ka- 

 olinite.f 



Origin of day deposits in general. — All clays and indeed most 

 shales (clay shales) may be said to have resulted primarily from the 

 alteration more or less completely carried out, of the felspar of 

 felspar bearing rocks. The disintegrated material resulting from 

 this alteration may either have remained where formed, still occu- 

 pying the position and retaining the lamination of the original 

 unchanged rock, or may have been subsequently removed b}^ the 

 ordinary eroding forces and deposited elsewhere as a bedded clay. 

 This removal, if merely for a short distance, may have been unac- 

 companied by any assorting of the clay and rocky materials; as for 

 instance is observed in the "kaolin" of the Cretaceous beds of 

 eastern New Jersey. Such an assorting appears however most 

 commonly to have taken place, the clay having been washed out 

 from the quartz and undecomposed rock fragments accompanying 

 it, having had more or less of foreign material mingled with it 

 during the process of sedimentation, and having thus resulted in a 

 bed of ordinary clay. Again in other cases the action of eroding 

 forces on the unaltered felspathic rocks may have resulted in a sed- 

 iment of powdered felspathic material which by subsequent altera- 

 tion has become a clay. In some one of these ways all true clays 

 would seem to haye been formed. Fragments [of felspar still re- 

 maining in many of them, and the alkaline ingredients sliown by 

 analyses, tesLifiy to this general origin. Of course bedded clays 

 may have been again and again removed and redeposited, mingled 

 with various imparities, or introduced as impurity into other sedi- 

 ■«■ Dana, p. 348. fDana, p, 361. 



