522 A TREATISE ON METAMORPHISM. 



TOTAL GAINS AND LOSSES IN WEATHERING, AND CHANGES IN VOLUME. 



The processes of oxidation, carbonation, and hydration involve great 

 additions of material and expansion in volume, provided all of the compounds 

 formed remain. Of these expansions in volume, that due to hydration is 

 the greatest. The added material is of course oxyg-en, carbon dioxide, 

 and water. The increases in volume due to the processes of oxidation, 

 carbonation, and hydration and their various combinations have been 

 worked out for each of the minerals (see Chapter V), and the results are 

 brought together in Table D on pages 395-408. It is seen there that the 

 expansion of volume with most of the silicates due to these processes and 

 their combinations usually varies from about 20 to 60 per cent, but in some 

 cases is 80 per cent or more. 



However, the processes of oxidation, carbonation, and hydration are 

 accompanied by solution of great quantities of materials, and consequently 

 the amount and the volume of the residual solid compounds are usually 

 far less than those of the original compound because of the abstraction of 

 a large proportion of the majority of the elements originally present and 

 their transfer to the surface waters or to the belt of cementation. 



As already fully noted, the calculations as to losses of elements thus 

 far made have been upon the supposition in a given case that one element 

 is constant; but in most cases, as already explained, it is highly probable 

 that a considerable portion of these elements also has been dissolved. 



On this hypothesis Merrill has brought together a number of computa- 

 tions upon the total losses of various rocks at different stages of weathering. 

 The calculated losses vary from 13.47 to 97.635 per cent. Supposing the 

 iron constant, disintegrated and partly decomposed granite from the Dis- 

 trict of Columbia has lost 13.47 per cent; supposing the aluminum con- 

 stant, a disintegrated and partly decomposed diabase from Medford, Mass., 

 has lost 14.93 per cent; a diorite from Albemarle County, Va , 37.51 per 

 cent; an argillite from Harford County, Md., 40.83 per cent; a diabase 

 from Spanish Gruiana, Venezuela, 39.51 per cent; a basalt from Kammer 

 Bull, Bohemia, 43.96 per cent; an altered pyroxenite, now soapstone, from 

 Harford County, Md., 52.46 per cent; a syenite from Arkansas, 55.28 per 

 cent; a basalt from Crouzet, France, 60.12 percent; an altered pyroxenite, 



