CHAPTER XIX. 



Observations on the geology of the country traversed by the 

 Expedition, 



The most prominent feature of the continent of North 

 America, is the great chain of the Rocky Mountains, evi- 

 dently a continuation of the Andes of the southern hemis- 

 phere, stretching parallel to the direction of the western 

 coast, from the Isthmus of Panama to the Frozen Ocean.* 

 Their summits, rising far above the limit of perpetual frost, 

 look down upon the wide plains of the Mississippi and its 

 tributaries, unvaried except by a low range of rocky hills, 

 commencing near the confluence of the Missouri and Mis- 

 sissippi, and running southwest to the Rio Del Norte. East- 

 ward of these, the surface again subsides to a plain, stretch- 

 ing to the foot of the great chain of the AUeghanies. This 

 last range, far less elevated and alpine than the Rocky 

 Mountains, traverses the continent in a direction parallel to 

 the Atlantic coast, from the gulf of St. Lawrence on the 

 northeast, to the confluence of the Alabama and Tombigbee 

 rivers, in the southwest. 



The AUeghanies, unlike the Rocky Mountains, have few 

 prominent summits; instead of conic peaks and a sharply ser- 

 rated outline, they present long and level ridges, rising in no 

 point to the inferior limit of perpetual frost, and in few in- 

 stances attaining that degree of elevation which is incompati- 

 ble with the growth of forests. 



In many particulars, a manifest resemblance is perceived 

 between the AUeghanies, and the comparatively inconsidera- 

 ble group, which we have denominated the Ozark mountains. 

 They are parallel in direction, making an angle of about forty 

 degrees with the great range of the Andes. In many parts 

 of both ranges, rocks of recent formation occupy the loftiest 

 summits, and are based on more ancient aggregates. It is 

 well known, that from the gneiss at Philadelphia, there is a 

 gradual ascent across strata more and more recent, to the 



* Mackenzis. «• The Stony Mountains, in lat. 68° 46, Ion. ISS" from 

 London ares" says Hearne, " of a craggy and tremeDdous aspect." 



