MOUNTAIN-MAKING. 797 



But the Adirondacks and Highland ranges, the Green Mountains, 

 and the Appalachians, together make up the Appalachian chain ; and 

 the latter is therefore a polygenetic mountain mass or system. 



On the Pacific side, the Wahsatch, Uintah, Elk, and other moun- 

 tains, are parts of an individual or monogenetic mountain range ; the 

 Sierra Nevada is another ; the coast ranges belong aggregately to an- 

 other ; the hills of uplifted Miocene in the Rocky Mountains, another ; 

 the Archaean Front Range of the Rocky Mountains, and whatever 

 ridges were one with it in origin, constitute another. The Rocky 

 Mountain mass is a combination of whatever individual ranges occur 

 in it (only those within the limits of the United States being yet 

 studied), and also of the results of a still later mountain-making move- 

 ment, that of the Tertiary, when the mountain mass was raised as a 

 whole. It is polygenetic. 



The monogenetic mountain ranges are of the following kinds : first, 

 those consisting of a combination of folded ridges, like the Green 

 Mountains, Appalachians, the Apennines, Carpathians, Coast Ranges 

 of the Pacific Coast ; secondly, those made up of one prominent mass, 

 with a granite core along the axis or toward one side, which granite 

 was made in the mountain-making process, as the Sierra Nevada ; 

 third, those of more or less upturned strata and extensive outflows of 

 igneous rocks, like the Mesozoic areas of the Atlantic border. All 

 gradations between these three kinds exist. Other more complex 

 structures are polygenetic combinations of two or more of these kinds. 



J. D. Whitney states, with regard to the Sierra Nevada, that the granite axis widens 

 southward, and volcanic phenomena increase northward. Granite makes nearly the 

 whole of its mass at the south end, from the Tahichipi Pass almost to Mariposa County; 

 but, north of this, up to American River, its area narrows, it being confined chiefly to 

 the summit and eastern side, the rest of the mountain region consisting of clay-slate, 

 mica and other schists, with quartzytes, serpentine, and some limestone, and some 

 granite in the mica schist; while north of American River the schists constitute nearly 

 the whole breadth, granite occurring only in occasional areas along the crest and east of 

 it ; and but little of the granite is gneissoid. Igneous rocks, on the contrary, increase 

 in amount northward. They cover part of the gravel beds in the several counties from 

 Mariposa to Plumas, a large part in Butte and Plumas counties, and almost the whole 

 surface north of Plumas, near whose borders stands Lassen's Peak, an extinct volcanic 

 cone, somewhat above 10,500 feet in height, and from which there is a series of cones, 

 extending northward, that culminates in Mount Shasta. The dip of the schistose rocks 

 is for the most part, according to Whitney, eastward, or toward the granite axis. The 

 range has its greatest height between the parallels of 36° and 37° 10', where are several 

 peaks over 14,000 feet. The western slope is mostly between 100 and 250 feet to the 

 mile, and the eastern, for a large part, 1,000 feet to the mile. The quartz veins of the 

 schists are the original sources of the gold ; and El Dorado, Placer, and Nevada, are the 

 great mining counties. Butte and Plumas afford much less gold, and probably because 

 the surface is so widely covered with igneous rocks. 



2. Continents. — Continents, in the earliest stage recognized by geol- 

 ogy, were great and almost featureless plateaus, separated by depres- 



