156 A TREATISE ON METAMORPHISM. 



As already noted, there are two zones of metamorphism, that of kata- 

 morphism and that of anamorphism, and the former consists of a belt of 

 weathering and a belt of cementation. 



The major part of the water entering the ground must finally reach the 

 surface. A small part may be combined with the rocks in the underground 

 course of the water. A small part may possibly penetrate deep within the 

 zone of anamorphism, but it is safe to say that at least 99 per cent of the 

 water entering the ground reappears at the surface in some manner. A 

 very large part of the water penetrating the soil is drawn to the surface 

 after having taken a longer or shorter journey in the belt of weathering. A 

 lesser part of the water joins the sea of ground water and takes a journey 

 of greater or less distance in the belt of cementation before it reaches the 

 surface. This journey may be merely from the top of a small hill to its 

 base, or it may be hundreds of kilometers. An exceedingly small fraction 

 of the water doubtless penetrates the zone of anamorphism, although, as 

 explained (pp. 665-668), the general movement is from rather than to this 

 zone. The underground journeys of water, whether the exceedingly 

 short ones within the belt of weathering or the longer journeys in the belt 

 of cementation or the zone of anamorphism, may be resolved into two 

 components, one parallel to the surface of the earth and one at right 

 angles to this surface. The first may be called the horizontal component, 

 the second the vertical component. On the average, the horizontal com- 

 ponent of the journey is many times longer than the vertical component. 



GEOLOGICAL AVORK OF GROUND WATER. 



From the foreg'oing it follows that the geological work of ground 

 water is favored by smallness of openings, by length of time, by pressure, 

 and by high temperature. Water enters the rocks mainly through the 

 smaller openings. A very large surface of the rock material is exposed to 

 water action. In so far as the water passes from the smaller openings to 

 the larger openings its geological work is lessened. The geological work 

 may be considered as directly proportional to the time. The smaller the 

 openings the greater the resistance, and therefore the greater the time for a 

 given journey. That the resistance runs up very rapidly as the openings 

 become small, and especiall}^ as they become capillary or subcapillary, has 



