90 



Cincinnati Society of Natural History. 



Weathering. 



As the percolating waters reached these rocks, the mineral 

 constituents were further altered, resulting in such weather- 

 ing products as chlorite, calcite, kaolin and iron hydroxide. 

 Chlorite is common in nearly all the rocks as an alteration 

 product of biotite and hornblende. It varies in character 

 from pale fibrous masses to large strongly pleochroic crystals, 

 and it fills the cracks of the other minerals, especially quartz 

 and feldspar. Calcite is found in a few granites near the 

 town of Rowlandville. Muscovite is formed often by the 

 bleaching of biotite, and the intermediate stages can be fol- 

 lowed, while kaolin results from the decomposition of the 

 feldspar. Iron hydroxide is very abundant in the decomposed 

 granites. 



