_Timber._—The trees worthy to be classed as timber are of three species—fir (_Abies Engelmanni_), Douglass Spruce (_A. Douglasii_), and yellow pine (_Pinus ponderosa_). The pine is the most valuable and the fir the most abundant. The fir grows upon the mountain slopes, above the level of 7,500 feet and forms thick-set forests. The total area which it covers is not far from twenty-five square miles. The spruce mingles with the fir at the lower edges of the forests; and the pine forms a few open groves a little lower down the slopes. It is to be doubted if the trees will ever be cut. Other timber of the same quality and superior in quantity lies between it and the settlements, and neither railroad nor mine nor town is likely to create a local demand. Coal, building stone, gypsum, and timber have no value for lack of a market, either present or prospective; gold and silver are not found; and there is little or no land that can be successfully farmed. Only for grazing have the mountains a money value. INDEX. Abajo Mountains, 67, 69, 152 Agricultural lands, 152 Alluvial cones and alluviation, 133, 139 Alpine sculpture, 36, 38 Altitudes of peaks and passes, 3, 117 Analogues of the laccolite, 98 Ancient rivers no larger than modern, 133 Antecedent drainage, 143 Arch, Bowl Creek, 45 , Crescent, 44 , Dana, 43 , G, 43 , Maze, 44 , Pulpit, 33, 147 Arches, Forces which produced laccolitic, 87 Aridity favorable to geological examination, 2, 98 of the Colorado Basin in former times, 120 Aubrey Sandstone, 8 Bad-lands, Sculpture of, 120, 140 Bischof, on contraction of igneous rocks in cooling, 76 Blue Gate flexure, 13 Sandstone, 4 Shale, 4 Bonneville, Outlet of Lake, 134 Bowl Creek arch, 45 Cañons of the Colorado as obstructions to travel, 1, 151 as evidence of arid climate, 120 Carboniferous strata, 8 Carriso Mountains, 69, 152 Circle Cliffs, 14 Cleavage, Slaty, not found, 66 , Vertical, produced by sapping, 55 Cliffs, Circle, 14 Climate, Arid, favorable to geological examination, 2, 98 , General influence of, on erosion, 103 , Influence of, on sculpture, 117 Coal, 5, 151 Colorado Basin, History of the, 84 Desert, 134 River, Origin of the, 85 Colors of sandstones, Local variation of, 7 Comminution of detritus aids transportation, 106 Competence, 110 Conditions of rock flexure, 83 Cones, Alluvial, 133 Consequent drainage, 143 Contact phenomena, 65 Contraction of igneous rocks by cooling, 75, 80 Corrasion, 100, 101 , Relation of, to declivity, 112 , to friction of flow, 109 , to transportation, 111 Cover of the laccolites, Depth of the, 86, 94 Crescent arch, 44 Cotta, Prof. Bernhard von, cited, 75 Cretaceous period, Disturbance at the close of the, 10, 85 rock series, 4 Cross-lamination, Inclination of, 7 Dana arch, 43