430 Expedition to the 



tent, its elevation at different points, and its connexion with 

 other rocks. On the southeast, secondary sandstones and de- 

 positions of coal are met with in some of the most elevated 

 parts of the Alleghany Mountains. The positive elevation of 

 the primitive mountains of New England, is, except at a 

 few points, scarce equal to that of the secondary in the 

 western parts of the state of New York. From the granitic 

 rocks, along the Atlantic coast to the secondary of the AUe- 

 ghanies, is an almost uninterrupted ascent. The clay slate, 

 and granite of the Washita, occupy nearly the lowest part of 

 the surface of the Mississippi valley. We are as yet, desti- 

 tute of barometrical, or other observations by which to de- 

 termine the actual height of the secondary on the sides of the 

 Rocky Mountains. Pike estimates the elevation of the plain 

 at the foot of the mountains, at eight thousand feet above the 

 level of the ocean. It is probable that this estimate of Pike's 

 far exceeds the truth, yet any one who considers the great 

 length and rapidity of the rivers which flow from that region, 

 the severity of cold in winter, the rapidity with which evapo- 

 ration is carried on in summer, the transparency and peculiar 

 aspect of the sky, will be convinced that those tracts are highly 

 elevated, and there is unquestionably good reason to believe 

 the secondary rocks along the eastern base of the Rocky 

 Mountains, have in many points, an elevation at least equal 

 if not much superior to the summits of the Alleghanies. In 

 the vertical sections delineated on the maps accompanying 

 this work, is a line indicating the supposed level of the primi- 

 tive ocean^ at the time when the secondary depositions ceased 

 to be formed; the line being intended to mark the greatest 

 elevation of secondary rocks on the sides of the Rocky 

 Mountains. 



This vast formation of secondary extending, as it probably 

 does from the Gulf of Mexico, to the northern ocean, and 

 from the bay of St. Lawrence to the Rocky Mountains, must 

 of necessity occupy in various parts, different and sometimes 

 great elevations. Like other great fields of similar forma- 

 tion, its borders are marked by high and broken ridges which 

 become less elevated and less frequent towards the centre. 

 Sandstone appears to be the basis and predominating rock, 

 occupying the Ijorders contiguous to the primitive and tran- 

 sition, and passing under the more recent secondary. In this 

 sandstone, on the outskirts of the secondary, have been found 

 most of the extensive coal beds hitherto known, also gypsum 

 and brine springs. 



