Excerpt from Preliminary Report on the Geology and Water Resources of Nebraska, West of the One Hundred and Third MeridianPi. XI has for its base a topographic map of the region, with contour lines 100 feet apart. These contour lines indicate heights above the sea, and they are numbered accordingly. The lines for every even 500 feet are made heavier than the others. Contour lines are lines of equal elevation, consequently they are drawn along the slopes of valleys like level irrigation ditches, in this case 100 feet apart vertically, extending up the side valleys, and running out around the points of projections. They encircle detached hills, and an isolated hill rising 500 feet above the plain would be indicated by five of the 100-foot contour lines. From the fore going statement, it will be seen that contour lines are crowded near together on steep slopes, but are widely separated on the plains and in the river bottoms. Thus, they indicate the shape of the land as well as its elevation.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.