every instance of their application. If the following remarks should on this account seem faulty, by a certain monotony and appearance of {273} repetition, we hope there are a few, who, for the sake of the facts detailed, will excuse any want of precision in the language which may have necessarily resulted from the unsettled condition of the nomenclature. [Illustration: VERTICAL SECTION on the PARALLEL of LATITUDE 41 degrees North _intended as a continuation of MACLURE'S third Section from the sea-shore to the summit of the Alleghenies_. VERTICAL SECTION on the PARALLEL of LATITUDE 35 degrees North _intended as a continuation of MACLURE'S fifth Section_.] No part of the earth, it is probable, presents a greater degree of simplicity and uniformity in the structure and conformation of its surface than North America. The mountain ranges are here distinct, forming each its own particular system, and preserving severally, through their whole extent, a similarity in external appearance, as well as in the structure and aggregation of the various rocks of which they are composed. The outlines of a physical delineation of the continent of North America would present, first, the great chain of the Rocky Mountains, evidently a continuation of the Andes of the southern hemisphere, stretching parallel to the direction of the western coast from the isthmus of Panama to the northern ocean. Their summits penetrating far into the regions of perpetual winter, look down upon the vast plains of the Mississippi and its tributaries; in which we distinguish a comparatively inconsiderable range of rocky hills, commencing near the confluence of the Missouri and Mississippi, and running south-west of the Gulf of Mexico, near the estuary of the Rio del Norte. Beyond these, the surface subsides to a plain, stretching eastward to the commencement of the great chain of the Alleghanies. The range of the Alleghanies, far less elevated and alpine than that of the Rocky Mountains, traverses the continent in a direction nearly parallel to the Atlantic ocean, from the Gulf of St. Lawrence, on the north-east, to the confluence of the Alabama and Tombigbee rivers, in the south-west. Compared to the Rocky Mountains, this range is without summits, presenting, instead of conic peaks, long and level ridges, rising in no point to the inferior limit of perpetual frost, and scarce in any instance reaching that degree of {274} elevation which is incompatible with the growth of forests.