tropicale, for suddenly, at a little over 2500 feet, everything 

 tropical vanishes and you find yourself among massed oaks of 

 tall stature, all loaded to the tips of their limbs with small 

 orchids and related epiphytes. These continue over the crest of 

 the range and down its west face, to march out onto the next 

 valley. This is an upland one, clothed in short open grass, on 

 which the oaks separate and stand about to create a perfect 

 parkland. We are in fact, here, back into the Parklands. The soil 

 of this valley is of a brilliant red; it contains lim nite or red 

 ocher which, when handled, will dye even the palms of your 

 hands for considerable periods. 



Beyond this valley there is another lower range of mountains, 

 and as you ascend them you run "back" through the Prairies into 

 the montane Scrub Zone once more, complete with huisadie and 

 some stunted mesquite, lowly cactus, sage, and many of our 

 other old friends. The next valley, the fourth (containing the 

 town of Ciudad del Mais), is arid to the point of desolation and 

 becomes even more nearly a desert as you approach the crest of 

 the fifth and last range. And there, at the summit of a low pass, 

 you may look out to the west over range upon range of moun- 

 tains and hills, at first slowly descending in altitude but then 

 mounting again into the endless ridges of the central plateau. 

 You are now at the highest point of the Sierra Madre Oriental, 

 and you are back in the "desert." It is puzzling; but I only hope 

 that by this time it will no longer be incomprehensible, and that 

 by combining the principle of vegetational belting by latitude 

 and of its zoning by altitude you may have realized that, as 

 you have been driving up from the hot, dry coastal plains of the 

 Gulf, you have returned, botanically speaking, to where you 

 started. 



EL SALTO DE NARANJO 



In the valley of this name there is a river which joins the Santa 

 Maria on the coastal plain at Valles and then flows on to the 

 Gulf at Tampico. It rises a short distance to the north in the 

 third range and descends into the valley by a fall named El Salto. 



Right: The Sierra del Sur. The upper slopes are clothed in 

 a short montane scrub; this becomes montane tundra and 

 then barren grounds and snowfields above. 



Below: The Beaded Lizard (Heloderma horridum), the only 

 relative of the Gila Monster — and also poisonous — is an 

 inhabitant of the lozver slopes of the western Sierras. 



