1008 A TREATISE ON METAMORPHISM. 



thus helping underground circulation, is more than probable, but that long 

 and important passages are produced wholly by solution is an assumption 

 which I think has not been verified. 



SIZE OF OPENINGS. 



Openings in rocks may be divided, upon the basis of size, into those 

 larger than capillary size, or supercapillary openings; capillary openings; 

 and those smaller than capillary size, or subcapillary openings. The mag- 

 nitudes of these openings are given on pages 134-137. The openings of 

 bedding parting, of faults, of joints, of conglomerates, and of tuffs are 

 frequently of supercapillary size. Many of these openings, and also many 

 of those of the sandstones, are of capillary size. All classes of openings 

 may be somewhere of subcapillary size, but many rocks, such as massive 

 igneous rocks and shales, may contain only subcapillary openings. 



VOI.V.MK OF OI'KXINOS. 



The total volume of the openings is dependent upon the number and 

 the size. The amount of pore space in rocks varies from less than 1 per cent 

 to more than 50 per cent. The total volume of the openings in a rock in 

 which they are so small as to be almost imperceptible and all subcapillary 

 may be as great as in a rock in which many openings are seen. For instance, 

 the pore space of a chalk may be as great or greater than that of a sandstone 

 or of a massive rock containing numerous continuous fracture openings of 

 large size. (See pp. 124-125.) In such cases the small size of the open- 

 ings is compensated by their vast numbers. 



CHEMICAL KE ACTIONS. 



As explained in the preceding chapters, especially in Chapter IV and 

 more fully in Chapters VII and VIII, the reactions of the zone of fracture, 

 or katamorphism, are those of oxidation, carbonation, hydration, solution, 

 and deposition. All are of great importance in connection with ore deposits. 

 In the belt of weathering all of these reactions, with the exception of depo- 

 sition, are vigorous. The sulphides, including the metals and the sulphur, 

 are likely to be oxidized. Oxides may be further oxidized. The metals 

 may be carbonated and hydrated and are likely to be dissolved upon 

 an extensive scale. While all of these reactions take place in the belt of 



