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GEOLOGICAL STRUCTURE OF NEW MEXICO. 



deem convenient and proper, or from attaching any portion thereof 

 to any other Territory or State: And provided, further, That, 

 when admitted as a State, the said Territory, or any portion of the 

 same, shall be received into the Union with or without slavery, as 

 their constitution may prescribe at the time of their admission." 



Under the old Spanish and Mexican governments, the boundaries 

 of New Mexico were exceedingly indefinite; but this act forever 

 fixes the territorial limits, and also settles the long vexed question 

 of the boundary of Texas. 



" New Mexico," says Dr. Wislizenius, in his excellent memoir 

 on the northern part of the Republic ; "is a very mountainous 

 country, with a large valley in the middle, running from north to 

 south, and formed by the Rio del Norte or Rio Grande. The valley 

 is generally about twenty miles wide, and bordered on the east and 

 west by mountain chains, continuations of the Rocky Mountains, 

 which have received different names, such as La Sierra Blanca ; 

 Los Organos, and Oscura, on the eastern side of the stream; and 

 the Sierra de las Grullas, De Acha, and De los Mimbres, towards 

 the west. The height of these mountains south of Santa Fe, may be 

 averaged between six and eight thousand feet, while near Santa Fe 

 and the more northern regions, some snow covered peaks are seen 

 rising probably ten or twelve thousand feet above the sea. The 

 mountains are principally composed of igneous rocks, as granite, 

 sienite, diorite, and basalt. On the higher mountains excellent pine 

 timber grows ; on the lower, cedars and sometimes oak, and in the 

 valley of the Rio Grande, principally mezquite. 



The main artery of New Mexico is the Rio del Norte or Rio 

 Grande, the longest and largest river ever possessed by Mexico. 

 Its head waters were explored in 1807 by Captain Pike, between 

 37° and 38° north latitude ; but its highest sources are supposed to 

 be about two degrees further north in the Rocky Mountains, near 

 the head waters of the Arkansas and the Rio Grande or Colorado of 

 the west. Following a general southern direction, it runs through 

 New Mexico — where its principal affluent is the Rio Chamas from 

 the west — and then winds its way in a south-eastern direction, 

 through the States of Chihuahua, Coahuila, Tamaulipas, and Texas, 

 to the Gulf of Mexico in 25° 56' north latitude. Its tributaries in 

 in the latter States are the Pecos, from the north ; the Conchos, 

 Salado, Alamo, and San Juan, from the south. The whole course 

 of the river, in a straight line, would be near twelve hundred miles; 

 but from the meandering of its lower half, it runs at least about two 

 thousand miles from the region of eternal snow to the almost tropical 



