By 1850 it was common knowledge that a railroad could be built along the Platte route, and it was believed that the mountains could be penetrated in several other places, but the process of surveying with reference to a particular railway had not yet been begun. It is possible and perhaps instructive to make a rough grouping, in two classes divided by the year 1842, of the explorations before 1853. So late as Frémont's day it was not generally known whether a great river entered the Pacific between the Columbia and the Colorado. Prior to 1842 the explorations are to be regarded as "incidents" and "adventures" in more or less unknown countries. The narratives were popular rather than scientific, representing the experiences of parties surveying boundary lines or locating wagon roads, of troops marching to remote posts or chastising Indians, of missionaries and casual explorers. In the aggregate they had contributed a large mass of detailed but unorganized information concerning the country where the continental railway must run. But Lieutenant Frémont, in 1842, commenced the effort by the United States to acquire accurate and comprehensive knowledge of the West. In 1842, 1843, and 1845 Frémont conducted the three Rocky Mountain expeditions which established him for life as a popular hero. The map, drawn by Charles Preuss for his second expedition, confined itself in strict scientific fashion to the facts actually observed, and in skill of execution was perhaps the best map made before 1853. The individual expeditions which in the later forties filled in the details of portions of the Frémont map are too numerous for mention. At least twenty-five occurred before 1853, all serving to extend both general and particular knowledge of the West. To these was added a great mass of popular books, prepared by emigrants and travellers. By 1853 there was good, unscientific knowledge of nearly all the West, and accurate information concerning some portions of it. The railroad enthusiasts could tell the general direction in which the roads must run, but no road could well be located without a more comprehensive survey than had yet been made. The agitation of the Pacific railway idea was founded almost exclusively upon general and inaccurate knowledge of the West. The exact location of the line was naturally left for the professional civil engineer, its popular advocate contented himself with general principles. Frequently these were sufficient, yet, as in the case of Benton, misinformation led to the waste of strength upon routes unquestionably bad. But there was slight danger of the United States being led into an unwise route, since in the diversity of routes suggested there was deadlock. Until after 1850, in proportion as the idea was received with unanimity, the routes were fought with increasing bitterness. Whitney was shelved in 1852 when the choice of routes had become more important than the method of construction.