Barrell — Physical Effects of Contact Metamorphism. 283 



ocean bottom. During the existence of the unaltered lime- 

 stone the impurities would be in part protected from further 

 decomposition by the stronger affinity of the lime for the 

 carbonic acid contained in the percolating waters, forming 

 soluble bicarbonates. After the solution of the lime, however, 

 the insoluble materials would form a residual clay soil, and as 

 long as their existence in that state continued, the water and 

 carbonic acid would tend to effect a change into hydrates and 

 carbonates. 



In Bulletin 148, IT. S. Geological Survey, page 389, are 

 three analyses of such a residual clay, and given below. The 

 three analyses furnish considerable data for the determination 

 of the combinations in which the elements exist, but such an 

 elaborate discussion is not necessitated by the work in hand. 

 They are by George Steiger and are as follows : 



ANALYSES OF CLAY, STAUNTON, VA. 



BCD 



SiO Q 55-90 3*09 52-81 



Ti0 2 -20 '04 -16 



Al 2 O s 19-92 3-96 15-96 



Fe„0 3 7*30 6-25 1-05 



FeO -39 -30 -09 



MnO_ none 



CaO.. -50 -30 -20 



MgO 1-18 -43 -75 



K 2 0_. 4*79 -28 4-51 



Na 2 -23 -20 -03 



H 2 at 110° 2-54 



H 2 above 110°. . 6'52 2*10 4-42 



P 2 5 .__ -10 -04 -06 



CO„ -38 -38 none 



99-95 



17-37 



80-04 



B. Residual clay from limestone, Staunton, Va. 



C. Portion of B soluble in weak hydrochloric acid. 



D. Insoluble portion of B. 



These analyses are particularly favorable for testing the 

 decomposition of the feldspars, there being large amounts of 

 silica, potash, alumina, ferric oxide and water present and 

 relatively small amounts of other components ; hence errors 

 in considering the state of combination of the latter will have 

 but a minor effect upon determining the form in which the 

 alkaline silicates are present. 



The fully hydrated form of aluminum silicates is kaolinite, 

 and this is the state toward which the weathered products of 

 the feldspars approach, the fully hydrated form of the ferric 



