California mines and minerals . lders are moreor less rounded, water-worn boulders of volcanic origin, brought intotheir present condition by running water. Volcanic breccia andvolcanic conglomerates are likewise designated by the term most common form of lava is the material of the light-colored,fine-grained, homogeneous beds, resulting from the consolidation ofthe ashes and volcanic mud. The lava of the tufaceous variety issometimes very compact, and has a metallic ring when struck, resem- THE MINERAL INDUSTRY OF CALIFORNIA 23 bling clink-stone (phonolite) in this respect. In this l
California mines and minerals . lders are moreor less rounded, water-worn boulders of volcanic origin, brought intotheir present condition by running water. Volcanic breccia andvolcanic conglomerates are likewise designated by the term most common form of lava is the material of the light-colored,fine-grained, homogeneous beds, resulting from the consolidation ofthe ashes and volcanic mud. The lava of the tufaceous variety issometimes very compact, and has a metallic ring when struck, resem- THE MINERAL INDUSTRY OF CALIFORNIA 23 bling clink-stone (phonolite) in this respect. In this lava, crystalsof glassy feldspar often occur. The lava is nearly always found capping (overlying) the gravel,but in some localities it occurs interstratified with the gravel. Beautiful dendritic markings (called photograph rocks) areoften found covering the lava. These markings are usually mistakenfor impressions of plants, but they are of inorganic origin, havingbeen formed by percolating waters, carrying oxide of manganese and. The Breakfast of a Mine-Surveying Party on the Mother Lode. oxide of iron, which substances have assumed the dendritic or tree-like form. Cement is a term of variable signification. In some districts itdesignates volcanic material of brecciated or conglomerated char-acter. In other localities it refers to a quartz (non-volcanic rock)conglomerate cemented by oxide of iron. Pipe-clay is more or less indurated clay, of non-volcanic origin,forming finely laminated beds. It generally occurs interstratifiedwith beds of sand, etc. The width of channel worked in hydraulicking varies from 150to 1,000 feet. The width of the deep rivers on top varies from afew hundred feet to several thousand. At Columbia Hill, Iowa Hill, 24 CALIFORNIA MINES AND MINERALS and other places, the rivers are from one mile to a mile and a halfwide. In some places, where the gravel deposits have a greatextent, laterally the width may be due to the confluence of two ormore streams or trib
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