WEATHEEING OF SYENITE AND PHONOLITE 



197 



The analyses on the preceding page from the work of Dr. J. P. 

 "Williams^ will serve to show the changes which have here taken 

 place in the transformation from (I) fresh syenite through (II 

 and III) intermediate stages of decomposition to (IV) a kaolin- 

 like residue. 



Eecalculating the numbers given in columns I and TV upon 

 the basis of 100, we obtain by further calculations the figures 

 given in columns V and YI and YII below, which represent the 

 proportional loss of each constituent, as before. 



Calculated Loss op Material 



OOKSTITUENTa 



Silica (SIO2) 



Alumina (AI2OS) 



^Ferric oxide (FeaOs) . . . , r 



Lime TCaO) , , 



Magnesia (MgO) ...... 



Potash (K2O) 



Soda (NaaO) 



Water (H2O) 



Total loss of original material. 



Lobs for Entiek 



EOOK 



37.28% loss 



0.00 



4.19 



L19 



0.67 



5.90 



6.16 



0.00 

 55.28^ 



VI 



Peroentagb 

 OP Each Con- 



8TITUKNT BAVED 



37.82 % 

 100.00 



13.83 



12.10 



17.90 



18.15 



2.89 



100.00 



VII 



Percentage 

 OF Each Con- 

 stituent LOST 



62.18% 



0.00 

 86.17 

 87.90 

 82.10 

 81.85 

 97.11 



0.00 



Here, as v^rith the granitic rocks, it will be noted there is a 

 gradual increase in the percentage of water as the decomposi- 

 tion advances, and a decrease in the amount of silica even more 

 pronounced. This last, as may be readily imagined, is due to 

 the absence of free quartz in the Fourche Mountain rocks. 



Weathering of Phonolite. — The phonolites of Marienf els, near 

 Assig, in Bohemia, have been described by Lemberg^ as weather- 

 ing into a bright-colored, porous, friable mass, the composition 

 of which, as compared with the fresh rock, is shown on the next 

 page. Each column, it should be stated, represents an average 

 of three analyses, I being the fresh and II the weathered ma- 

 terial, while in III, IV, and V are given the percentage calcula- 

 tions of gain and loss, as before. 



^ Ann. Bep., Vol. II, 1890, Arkansas Geol. Survey. 



2 Zeit"%r Deutschen Geol. Gesellschaf t, Vol. 35, 1883, p. 559. 



