328 University of California Publications in Geology [Vol. 7 



purposes of the term breccia as applied to alluvial fan deposits 

 owing to its comprehensive or generic meaning; and (3) to 

 suggest a petrographical name for such deposits. 



Ancient Alluvial Fan at Battle Mountain. Nevada. — My 

 attention was drawn" particularly to the question of a suitable 

 designation for alluvial fan deposits in the course of a recent 

 visit to Battle Mountain, Nevada. The rocks of Battle Mountain 

 consist chiefly of quartzite, shale and limestone of Paleozoic age. 3 

 These are traversed by dykes of igneous rock prevailingly of 

 rhyolitic type, some of these dykes having an abundance of large 

 phenocrysts of quartz. The rock of the dykes is in some cases 

 quite fresh but in other cases it is decomposed and is then 

 charged with copper ores to such an extent as to have stimulated 

 much prospecting. In the northeastern portion of the mountain 

 with which I became particularly familiar the Palaeozoic strata 

 dip prevailingly to the eastward, bat in some localities westerly 

 dips were also observed. According to the report on the Geology 

 of the 40th Parallel 4 the prevailing dip of the mountain, pre- 

 sumably farther west, is westward, thus indicating that the 

 general structure is anticlinal. 



Resting unconformably on the upturned edges of these strata, 

 and occurring chiefly as a mesa-like cap on various hilltops, is 

 a later formation composed of angular fragments of the under- 

 lying rocks, but so thoroughly silieihed and cemented that it is 

 one of the hardest and most resistant formations of the district. 

 Here and there in the midst of the angular fragments there may 

 be found well water worn pebbles which have probably been 

 derived from some earlier conglomerate. The fragments range 

 in size up to several inches in diameter, and it is evident that 

 any sorting action to which they may have been subjected in the 

 process of accumulation has been an inefficient one. There are 

 many holes or cavernous spaces in the rock which have the same 

 range of dimension as have the fragments which make up the 

 rock. These spaces were originally probably occupied by frag- 

 ments of limestone which have been dissolved out by meteoric 



a Hague and Emmons (Geology of the 40th Parallel, vol. II, p. 666, et 

 seq.) refer the limestone to the upper coal measures and the quartzite to the 

 Weber quartzite on the basis of fossils found in the limestone. 



■* Loc. cit. 



