468 GEOLOGICAL EXCURSION TO THE ROCKY MOUNTAINS. 



From Lamy a branch runs north across Tertiary beds (Santa Fe 

 marls) 40 miles (65 km.), to Santa Fe, one of the oldest settlements in 

 the United States. Like many other Spanish towns of the Southwest, 

 it occupies the site of an Indian pueblo. 



The road now passes into the Laramie coal bearing rocks, in which 

 some mines have been opened not tar from Ortiz. The beds are, how- 

 ever, much broken by eruptive rocks, and the coal in some eases has 

 been changed to anthracite. In the valley to the south, around the 

 Placer mountains, is a considerable accumulation of gold-bearing 

 gravels which might be profitably worked if it were not for the absence 

 Of water. 



To the north of Los Cerrillos, in the hills of the same name, tur- 

 quoise is found in rhyolite. The mines from which this mineral is 

 obtained are supposed to have been worked by the Aztecs before the 

 advent of the Spaniards. 



Beyond Wallace the road enters the valley of the Rio Grande del 

 Norte. This stream takes its rise in the various mountains which sur- 

 round the great interior valley of San Luis Park. After leaving this 

 well watered and fertile valley it passes through narrows formed by 

 coulees of basalt into the arid regions of New Mexico. To one coming 

 from the east the portion of the valley followed by the railroad has a 

 general aspect suggestive of that of the Nile. The river flows in a 

 broad alluvial bottom, bounded by low blulfs at considerable distances 

 back from the river. In the early summer, when the snows melt in the 

 mountains, its waters spread out over the bottoms and leave a thin 

 deposit of fine alluvial soil, which soon becomes brilliantly green with 

 growing crops and fruits. As the river falls, the heat of summer grad- 

 ually turns this veidure to a somber yellow or drab, except in a few 

 favored spots. The old-world aspect of the valley is heightened by 

 the quaint old Spanish towns, Largely built of adobe or sun-dried 

 bricks, and still more by the villages of the Pueblo Indians, built of 

 stone, but plastered over the surface with mud. 



[By c. K. Gilbert.] 



East of Albuquerque stand the Zandia mountains 90 overlooking 

 the Eio Grande with a bold mural front, even and straight, and little 

 gashed by canyons. From the water to the crest the rise is 7,000 feet 

 (1^100 m.). Except the crest the whole front is Arehean, but from end 

 to end there is a cornice of Carboniferous limestone a few hundred feet 

 thick, that by its continuity shows the whole was raised in a single 

 unshattered mass. The eastern face is of easier slope, but is less regu- 

 lar. The limestone band, that forms the persistent and almost level line 

 of crest, is the edge of an east \\ aid-dipping bed that is succeeded in that 



