MANNER OF DEPOSITION. 95 



same neighborhood. When the processes of solution and deposition go on 

 simultaneously their coexistence is no doubt due to local differences of 

 temperature and pressure. Changes in the amount of percolating water 

 and other circumstances may also bring about deposition where solvent 

 action once prevailed, or vice versa. As before stated, the dissolving of the 

 limestone in particular directions has been owing in great measure to the 

 antecedent crushing of the limestone. 



Connection of caves with fissures, ore bodies, and each other in Eureka. The C3VeS ill Elll'eka 



District are of more frequent occurrence near the surface than they are in 

 depth, no caves of any importance having been found below 1,000 feet. 

 They are almost invariably connected with some fissure, and are also often 

 connected with one another by fissures and open pipes. No oxidized ore 

 body of any great magnitude is found without a cave above it, which is 

 usually proportionate in size to the ore body, but all caves are by no means 

 accompanied by masses of ore. Though the , caves are very irregular, 

 having ramifications in all directions, they form a system or systems which 

 have a downward trend approaching the foot wall of the formation in which 

 they are found. As the ore bodies are associated with caves their deposi- 

 tion is, of course, similar. 



Action of water in the caves. — The roof and sides of the caves sometimes pre- 

 sent the appearance of a chamber blasted out of the solid rock, and do not 

 show any signs of the action of water. This, however, is rarely the case, 

 and is a result of the falling in of the roof and sides as they were originally 

 formed. The action of the. water can often be observed upon some of the 

 sides of the bowlders, which in such instances always cover the bottom of 

 the caves. Usually the surfaces of the caves show the effect of the cor- 

 roding action to which they have been subjected; the rock is hollowed out 

 in cup-like forms, which are roughened and indented with lines caused by 

 the difference in solubility of the various parts of the rock. These surfaces 

 have a light-grayish color streaked with white, and in the neighborhood of 

 ore are more or less stained with ferric oxide. 



Formation of aragonite and cal ite in the caves. Clusters of ai'agOnite aild Calcite 



crystals are frequently found covering large areas on the roof and sides. 

 Although water is found dripping from the roof of some of these caves it 



