UNIVERSALITY OF CEMENTATION. 565 



instances of very large openings below the level of ground water are fur- 

 nished by the caves in the lead and zinc district of Missouri. Here, in 

 consequence of extensive pumping operations, the level of ground water has 

 been lowered from a few meters to 45 to 60 meters. At various places below 

 the level of ground water caves of considerable magnitude have been found, 

 some nearly 60 meters in length and with rooms 12 to 15 meters in width. 

 These caves are lined with crystals of calcite. The faces are perfectly 

 clear. It is almost certain that the crystals continued to grow until the 

 level of ground water passed below them. The caves are, in fact, like 

 gigantic geodes with great scalenohedral crystals, some of them a half meter 

 or more in length, projecting- everywhere from the walls. No stalactites 

 or stalagmites are found, or any of the other peculiar phenomena so 

 characteristic of caves above the level of ground water in the belt of 

 weathering. These caves, before transferred from the belt of cementation 

 by the lowering of the level of ground water, were being filled, and had 

 the process continued sufficiently long - there would have been formed great 

 masses of crystalline calcite analogous to the masses of that mineral which 

 are sometimes elsewhere found. 



Concluding from the geological facts observed, it seems perfectly clear 

 to me that the fundamental fact of the part of the zone of fracture between 

 the level of ground water and the zone of anamorphism is that cementation 

 is the most characteristic process, and therefore the one which properly 

 gives its name to the belt. 



BOUNDARIES OF BELT OF CEMENTATION. 



It has been explained (pp. 409-411) that in different areas the level of 

 ground water is at different depths from the surface, varying from zero to 

 300 meters, and exceptionally to a thousand meters. 



It has been shown that the level of the upper surface of the ground 

 water is not horizontal, but undulating, and that the undulations of the 

 level of ground water roughly follow the topography, as shown by the fact 

 that upon many hills and mountains wells reach water of saturation at the 

 very moderate depths of a few meters to 50 meters. A topographic map 

 of a region is to a certain extent a map of the level of ground water, but 

 the latter shows less accentuated contours. The elevation of the contour 

 of the ground water at a given place is less than the elevation of the 



