BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 8 pp. 157-168 February 22, 1897 



WEATHERING OF MICACEOUS GNEISS IN ALBEMARLE 



COUNTY, VIRGINIA 



BY GEORGE P. MERRILL 



(Read before the Society December 81, 1896) 



CONTENTS 



Paee 



Introduction 157 



Petrographic features of the fresh rock 158 



Physical manifestations of weathering. 158 



Chemical analyses and their discussion 159 



Cause of red color of the soil 161 



Zeolites in the fresh rock and their possible origin 162 



Use of the term weathering 163 



Formation of zeolites in soils 164 



Efficacy of zeolites as conservators of potash 165 



Proportional amounts of soluble matter in fresh and decomposed rocks 166 



Possible form of combination of soluble constituents 168 



Introduction. 



In previous papers the writer has endeavored to show the changes 

 taking place in the preliminary stages of rock-weathering as illustrated 

 in the post-Cretaceous and post-Glacial disintegration of the granites of 

 the District of Columbia and the diabase of Medford, Massachusetts.* 

 The purpose of the present paper is to discuss the results of similar pro- 

 cesses, operating for longer periods, and incidentally to refer to other 

 matters with which the subject is closely affiliated. 



The material selected for investigation is a highly micaceous, feldspar- 

 rich gneissoid rock and its residual clay, occurring at North Garden, in 

 Albemarle county, Virginia. The region lies to the west of the Cretaceous 

 submergence, the accumulated gravels of which enabled us to set an ap- 

 proximate time limit to the weathering manifested in the District of 



* Disintegration of the Granitic Rocks of the District of Columbia, Bull. Geol. Soc. Am., vol. 6, 

 1S95, pp. 321-332, and Disintegration and Decomposition of Diabase at Medford, Massachusetts, 

 ibid., vol. 7, 1896, pp. 349-362. 



XXIII— Bull. Geol. Soc. Am., Vol, 8, 1896 (157) 



