LIME DEPOSITS OF CA\^ERNS 345 



ceased, and spasmodic but fiercely rushing streams cut the arroyo 

 to its present depth, exposing in either wall the irregularly alter- 

 nating beds described." (Merrill-35 : 348.) Two highly carbonated 

 springs still occur in the bottom of the canyon, building small beds 

 of tufaceous material. 



Considering the nature of the country rock in this and the Ari- 

 zona localities, and the highly carbonated character of the springs 

 still remaining, one is led to regard the water as magmatic or juve- 

 nile, bringing its burden of lime from greater depth. 



In Algeria, North Africa, province of Oran, deposits of this 

 type occur, covering an estimated area of about 12 acres. The 

 formation consists of strata varying from 6 inches to 4 feet in thick- 

 ness and separated by beds of compact travertine. The deposits are 

 of Quaternary age, resting unconformably upon Middle Miocenic 

 limestones and sandstones. Similar deposits are also found in 

 Persia. 



A significant fact bearing on the mode of deposition of these 

 formations is that these deposits occur in regions of comparatively 

 recent volcanic activity, and it is highly probable that the onyx 

 marbles were deposited in heated waters and possibly under the 

 surface of a pool or shallow lake, which would prevent too rapid loss 

 of COo, resulting in ordinary porous travertine. Such travertine 

 was formed after the periodic draining of the lakes. 



Underground Deposits of Lime. Caverns are especially noted 

 for the extent and variety of their deposits of calcium carbonate. 

 In certain Missouri caverns once submerged by a rising of the 

 ground water, i. e., caverns formerly situated within the belt of 

 cementation, lime was deposited as crystals of calcite, lining the 

 walls, as in huge geodes {ajite, p. 177). Caverns within the belt 

 of weathering and hence not filled by the ground water are charac- 

 terized by the deposition of stalactites and stalagmites normal to 

 such caverns. These are formed by the water percolating through 

 the limestone of the roof of the cavern and becoming suspended in 

 drops. Partial evaporation of the water in the dry air, or the 

 escape of the CO2 which held the lime in solution, results in the 

 formation of a ring of lime for each drop, from the base of each of 

 which a second drop becomes suspended, with the subsequent addi- 

 tion of a second calcareous ring at the bottom of the first one. By 

 this process a hollow tube is formed, which grows by addition be- 

 low, and increases in thickness by successive layers added by the 

 water flowing on the outside of the tube. After a time the external 

 deposits increase to such an extent that they will cover the opening 

 of the tube, or this may become closed by deposits within it. The 



