VEINS. 413 



If a country be composed of rock of feeble and variable tenacity, the 

 tendency of the ground near the surface to break up into irregular frag- 

 ments will be much greater than where the country is firm and homogene- 

 ous, and the formation of chambers of ore close to the original surface is 

 the more to be expected. The ore bodies which were found near tlie crop- 

 pings of the Comstock Lode were of this description, and so are most of 

 the more superficial cinnaV)ar deposits of California. 



I propose for tliese irreguhir bodies found at the croppings of veins 

 the name cap chambers, to distinguish them from the lateral ore bodies of 

 chambered veins. The term vein chamber then. includes cap chambers as 

 well as lateral chambers. 



So far as we know anything of the mechanical conditio: is of ore depo- 

 sition, it appears from the foregoing paragraphs that many deposits which 

 now appear as simple fissure veins must once have included cap chambers, 

 and must consecpiently have come under the definition which I have pro- 

 posed of a chambered vein. The cap chambers in these cases must have 

 been removed l)y erosion. Where ore deposition has continued until all 

 available crevices were filled, as has sometimes but not always been the 

 case, it is evident that cap chambers will contain a comparatively large 

 amount of ore, often more than will be found within an equal vertical inter- 

 val far from the surface, where the fissure system is more simple. Such 

 was the case, for example, on the Comstock lode. Such also may have been 

 the case on the gold belt of California, and the immense amount of aurifer- 

 ous gravel would then not represent the erosion of contracted quartz veins, 

 such as are now being mined, but of tlie cap chambers of the veins This 

 hypothesis greatly reduces the amount of general erosion wliich the exist- 

 ence of these gravels would imply. 



Tlie terms simple fissure vein, group of paraUel veins, linlced veins, and 

 chambered veins probably include nearly all species of deposits except- 

 ing sedimentary l^eds and placers. It is of course easy to imagine irregu- 

 lar bodies of ore unconnected with any fissure system, but it is doubtful 

 whether such really occur in nature. If these terms should be adopted, the 

 names impregnation, stockwork, pocket, etc. would be understood to refer 

 only to the structural character of specific portions of deposits, and not to 

 the form of any deposits as a whole. 



