EOCKY MOUNTAINS 375 sq. m., lies west of the Mississippi, and this vast area may be defined as the Rocky mountain re- gion. This great group of ranges extends south- ward through Mexico and Central America to the isthmus of Darien, and northward into Brit- ish America and Alaska to the Arctic ocean. The great chain of the Andes of South Ameri- ca is an extension of the same group, and in a general view they all form one great system. Not till within the present century was there any definite understanding of the geography of the Eocky mountains. Upon the old maps the mountain ranges were shown by a single line of hachures, with a few minor ranges branching off, the whole trending nearly N. and S., or rather W. of N. and E. of S. The first important government expedition was that of Lewis and Clarke, which in 1804-'6 passed up the Missouri river to its source, crossed the main divide of the Eocky mountains, and fol- lowed the Columbia to its entrance into the Pacific ocean. Although this expedition was a great achievement in a geographical point of view, taking into consideration the time and the means at its command, yet much of the information it obtained was very vague and limited to a narrow belt across the northern portion of the country. Lewis and Clarke, however, fixed pretty well the positions of the Missouri and Columbia rivers. The next ex- plorer was Major Z. M. Pike, who in 1805-' 7 crossed the country further south, and discov- ered the head waters of the Arkansas and the lofty peak which now bears his name. He crossed the divide into the Great Basin. In 1819-'20 S. H. Long was sent out by the gov- ernment with a well equipped party, compri- sing not only topographers, but also geologists and naturalists, including Thomas Say. After Long came Bonneville, Eoss Cox, Schoolcraft, Nicollet, Fremont, and others, all of whom added to the store of knowledge in regard to this great area. From 1844 to 1860 more than 20 expeditions were sent out, with the object of determining the best route for a rail- road to the Pacific. In 1853 congress passed the bill making appropriations for the deter- mination of the most practicable route for a railroad from the valley of the Mississippi to the Pacific coast. No expense was spared in equipping expeditions, which traversed the country from E. to W., at various points from lat. 49 to the southern boundary of the Uni- ted States. The information thus obtained was embraced in a large series of maps and reports (13 vols. 4to). Yet up to 1865 no portion of the great Eocky mountain region had been ex- amined with such care and detail as to render the maps anything more than approximately correct. The information thus obtained could only be placed on a map projected on a small scale, where an error of five or ten miles would be overlooked. Within the past ten years sev- eral expeditions have been organized with the object of working out certain areas with con- siderable detail, including topography, geology, and natural history ; and more definite knowl- edge of the Eocky mountain region has been obtained within that period than in all the pre- vious years. To convey an idea of the plan and growth of the development of the great area west of the Mississippi, it is only necessary to suppose it to have been originally a vast plateau, out of which have been evolved the different ranges of mountains as if they had been lifted by volcanic action. Indeed they appear as wrinkles on the earth's surface, and were probably produced by the contraction of its crust in the process of cooling. This may be understood more clearly by examining some of the barometrical profiles which have already been constructed across the continent. In pro- ceeding westward along the Missouri river, the ascent is gradual, at first not more than one foot in a mile, but steadily increasing until the base of the mountains is reached, when the rise becomes suddenly 50 to 100 ft. or more in a mile. The profile of the Pacific railroad shows that Omaha on the Missouri river is 1,060 ft. above sea level, while at Co- lumbus, 91 m. by rail westward, the elevation is 1,470 ft., showing an ascent of about 4 ft. in a mile. At Cheyenne, 516 m. W. of Omaha, the elevation is 6,075 ft., showing an ascending grade from Omaha of nearly 10 ft. in a mile. This entire distance is over an apparently level plain, most of the way by the valley of the Platte. From Cheyenne to the highest point along the line of the railroad, at Sherman, 8,271 ft., the distance is 38 m., when the grade suddenly increases to over 66 ft. in a mile. The profile along the Kansas Pacific railroad, from Kansas City on the Mis- souri to Denver, shows similar results. At Kansas City the elevation is 764 ft. ; at Den- ver, 639 m. W., 5,197 ft., making an average ascent of nearly 7 ft. per mile across an ap- parently level, treeless plain. A few miles W. of Denver, the great Colorado or Front range seems to rise abruptly out of the plains, its summits reaching the line of perpetual snow. The great mass of the Eocky chain lies W. of the 105th meridian. The united ranges trend about 20 W. of N. Along the eastern slope the smaller or minor ridges have a trend more to the northwest, so that they constantly die out in the plains, giving to the eastern side the appearance of an echelon arrangement. As the small ridges run out, they often present a fine example of an anticlinal, as seen on the Cache a la Poudre river. From the notches in the outline of the ranges, the Platte, Ar- kansas, and many other rivers open into the plains. About the source of the Missouri the main chain is 9 of longitude further W. than in Colorado. In this broad space and to the eastward are numerous outliers, as the Black hills, Big Horn, Bear's Paw, Judith groups, &c., all more or less distinctly connected with the main chain. The Black hills are connected with the Laramie range, near the Eed Bnttes, by an anticlinal valley, while the Big Horn
