A Geological Map of the United States and British Provinces of North America (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1853 Excerpt: ...to the distances is observed, and the curve of the earth is considered. Topography is one of the most important points for a geological map; for, without it, it is materially impossible to describe and understand the orographical structure of a country. The geological structure of the Alps, the J ura, and Auvergne, have been exactly described and understood, because there are good topographical maps of these regions. Unhappily, America has as yet no good topographical maps; and, notwithstanding the attempts at orographic description which have been made upon the Alleghanies, the degree of exactness of these theories cannot be determined, nor to what part of these mountains they may be applied, except from the sections made by geologists who have been engaged in this study. In the geological map here given, there are no topographical indications, for the very simple reason that, being unable to make them exact from the want of topographical maps, I preferred to omit them entirely. But I have written near the places occupied by different chains of mountains the names of these chains, in order to give an idea of their relative position, and, also, that I may class these mountains according to their relative age; that is, following the chronological order of their appearance. ERUPTIVE AND METAMORPHIO ROCKS. DIRECTIONS or MOUNTAIN muons. Hitherto we have described the stratified rocks whose successive beds cover the larger part of the surface of the United States and of the Provinces. There is a second category of unstratified rocks, whose masses, coming from an unknown depth in the interior of the globe, rise, like irregular columns, and reach the surface, generally forming the summits of the highest mountains. These rocks, of igneous origin, have been inserted...