380 ROCKY MOUNTAINS and 41st parallels, where it varies from 800 to 1,000 in. In this belt are the greatest num- ber of lofty peaks, including the highest por- tion of the Sierra Nevada. Among the numer- ous ranges of the Rocky chain are many val- leys and plateaus, varying from a few acres to hundreds or even thousands of square miles. Sometimes they are formed by erosion or by depression ; many of them are ancient lake basins. In all the great mountain districts of the west are thousands of these openings, into which settlements have already penetrated. In the San Juan mountains is Baker's park, with an extensive settlement of miners, and in the surrounding mountains are some of the richest silver mines in America. The North, Middle, and South parks, in Colorado, are areas of depression underlaid with sedimentary strata and walled on every side by lofty mountain ranges ; they are really old lake basins. The North park has a comparatively level surface, and an average elevation of 8,000 ft. S. of this, and only separated by a rather low moun- tain range, is the Middle park, which is much larger and far more rugged; indeed, there is very little of what might be called plain coun- try, but a succession of high ridges, many of which are of volcanic origin. The average elevation is about 7,500 ft. Still further S., but separated by a much wider belt of moun- tainous district, is the South park, which is mostly a plain, with an average elevation of about 9,000 ft. In these parks there is frost every month of the year. (See COLORADO.) San Luis valley, in southern Colorado and northern New Mexico, has an average eleva- tion of 7,000 to 8,000 ft. The Llano Estacado of Texas and New Mexico averages 3,200 to 4,700 ft. above sea level; the Colorado plateau in Arizona, 5,500 ft. ; Salt Lake valley, Utah, 4,200 to 4,500 ft.; Laramie plains, Wyoming territory, 7,000 ft. ; Snake river plain, in Ida- ho, 4,000 to 4,500 ft. ; Sevier lake basin, Utah, 4,700 ft. ; 1 1 uniliul.lt river basin (Lassen's mea- dows), Nevada, 4,200 ft. ; Carson river basin, 8,800 ft. ; Walker's river basin, 4,100 ft. ; and Mojave river basin, California, 1,100 ft. Com- paring the mountain plateaus or basins of the Rocky mountain region with some of those in the Andean region of South America, the differ- ence of elevation is very great. The Antisana plateau of South America is 13,451 ft.; the basin of Santa F6 de Bogota, 8,413 ft.; and the basin near Lake Titicaca, 12,853 ft. Per- haps as great an extent of plateau is comprised in the belt between the 38th and 44th parallels of latitude as in any other portion of the Rocky area. Through this belt the Pacific railroad passes. From Omaha to Cheyenne the track lies nearly all the way on the most modern tertiary formations. From Cheyenne west- ward the road crosses the Laramie range, the highest point, Sherman, being 8,271 ft. After passing over about 15 m. of granite rocks, it descends into the Laramie plains. Thence to the Wahsatch range in Utah no more granitic rocks are met with, only cretaceous or tertiary. In crossing the water divide at Creston, 7,030 ft. high, the stranger would not suspect that he was passing from the Atlantic to the Pacific slope. The road runs through the Wahsatch range at right angles, in the channel of the Weber river, with only 4 m. of granitic rocks, so that from Omaha to Ogden only about 18 m. of metamorphic rocks are met with. Thence the Central Pacific crosses the Salt lake basin, enters the Humboldt valley, and really meets with no mountains until it reaches the Sierra Nevada, where a most formidable obstacle pre- sents itself in a massive granite mountain range, which however is crossed at an elevation of only 7,042 ft. According to Messrs. Blake and King, there are seven longitudinal zones or belts of mineral deposits in the west, following the pre- vailing direction of the mountain ranges. Mr. King says : " The Pacific coast ranges upon the west carry quicksilver, tin, and chromic iron. The next belt is that of the Sierra Nevada and Oregon Cascades, which upon their W. slope bear two zones, a foot-hill chain of cop- per mines, and a middle line of gold deposits. These gold veins and the resultant placer mines extend far into Alaska, characterized by the occurrence of gold in quartz, by a small amount of that metal which is entangled in iron sul- phurets, and by occupying splits in the up- turned metamorphic strata of the Jurassic age. Lying to the east of this zone, along the E. base of the Sierras, and stretching southward into Mexico, is a chain of silver mines, con- taining comparatively little base metal, and fre- quently included in volcanic rocks. Through middle Mexico, Arizona, middle Nevada, and central Idaho is another line of silver mines, mineralized with complicated association of the base metals, and more often occurring in older rocks. Through New Mexico, Utah, and western Montana lies another zone of argentif- erous galena lodes. To the east again the New Mexico, Colorado, Wyoming, and Montana gold belt is an extremely well defined and continu- ous chain of deposits." It has usually been understood that there is no coal in the true coal measures in the Rocky mountain district ; but of late years a few thin seams have been reported as occurring in the south and south- west. In Colorado, Wyoming, Utah, Montana, and New Mexico, vast areas are underlaid by thick beds of coal belonging to the cretaceous and tertiary groups. In southern Colorado, New Mexico, and the interior of Utah, thick and important beds of coal are found in the cretaceous group, while along the E. slope of the Rocky chain in Colorado, as at Raton hills, Cafion City, Colorado Springs, Golden City, and northward, are numerous coal beds be- longing to the lignitic group, eocene tertiary, which are now wrought to a large extent. In the northwest the lignitic area covers at least 100,000 sq. m. Along the Union Pacific rail- road are coal beds of the same age, without which the railroad could not exist. Not less
