This whole inland artM in precoloni.il days nuisl have been 

 remarkable; it appears to have been kept in somelhinj* like its 

 early condition by means of fue. both naturally generated by 

 lightnins and artificially by the Amerindians The Spaniards 

 brought in longhorn cattle and horses, both of which went feral 

 in droves and which for a period much altered the landscape, 

 eating out the underbrush and permitting grass to lake over. But 

 these too. like the Amerinds, died away, and the natural flora 

 began to take over again. Deer also multiplied and other more 

 docile strains of cattle were introduced, and in the Welder area 

 —now protected — a limited number of the latter are allowed to 

 roam at will to keep down the underbrush and to permit some 

 grass to survive. There is now estimated to be about one of the 

 small Texas White-tailed Deer per eight acres hereabouts. Thus 

 this bit of territory, it is believed, once again looks not too dif- 

 ferent from what it did before the European came to upset the 

 biological balance (though it is thought that it was even then 

 not a climax type) that is supposed to have prevailed under the 

 Amerindians. 



This northern half of the triangle (see map) is formed of three 

 great steps— the Nueces Plain inland above the low Bordas 

 Escarpment, the main coastal plain, and the coastal lowlands 

 strip of marshes. The second devolves to the south into a large 

 sand plain. The valley of the Rio Grande, from its mouth to the 

 present town of Rio Grande, is rich alluvium and is now exten- 

 sively cultivated, but west of this point it becomes very arid on 

 both sides of the river. Here we have entered the Desert Belt 

 which forms an expanding wedge to the east but is. as it were, 

 plugged by the delta and the intensively cultivated lands of the 

 river valley. When these lands are left fallow they develop a 

 desert form of diaparral without any grasses, with many cac- 

 tuses and a tangle of small-leafed, stunted bushes. Proceeding 

 south from the river toward the Mexican Sierras, one encounters 

 a very interesting development. 



DESERT BARRIER 



First, there is a wide reach of cultivated fields and then sud- 

 denly a narrow desert belt. On the main road south from Mata- 

 moros and Brownsville this belt is only about twenty miles wide 

 and might well be missed by anybody except specialists, for it 

 doesn't look very different from the scrublands to the north. 

 The vegetation is. however, reduced to a few kinds of lowly 

 bushes and clumps of hard-stemmed herbage, with many small 

 cactuses. The ground is bare and stony, and almost all signs of 

 wildlife disappear, at least during the day. By night a paltry 

 fauna of small animals, mostly rodents, makes its appearance. 

 But. despite the fairly abundant food supply that these offer to 

 predators, everything else seems to shun this strip — even foxes, 

 coyotes, skunks, and others that are abundant to both the north 

 and the south. The true deserts form one of the major "breaks " 

 in the distribution of plants and animals between the tropical 

 and subtropical on the one side, and the temperate and boreal 

 on the other. The animals — even the insects here. I am told — 

 "know" this, and simply will not cross this barrier and do not 

 even enter it to feed 



South of this sterile strip we enter an entirely new land 

 again. At first sight this looks even more like the Northern Scrub 

 Belt in its subforested or chaparral form. Flowering shrubs, many 

 with broad leaves, mimosas and acacias, and the flowering cac- 

 tuses begin again; but there is a difference. Most of the plants 

 are even more spiny, and broad-leafed bushes, shrubs, and even 

 small trees gather in greater profusion. The cactuses get bigger. 



The Ghost Crab, adapted to the sandy shallows oj llic 

 Gulf coast, resorts to the beach in search of food and can 

 live for long periods out of water. 



and one lot of herbs after another leaf and flower throughout the 

 year and even in dry periods. The most notable bush is the 

 Nakahuita with its covering of beautiful, four-petaled white 

 flowers, while the undergrowth is given a pale bluish cast by the 

 little Saniso bush. This continues with some variation until one 

 climbs in among the flat-topped low mountains of the ancient 

 coastal range. At this point somewhat intensive agriculture 

 begins again along the modem highway; but if you walk or ride 

 back a mile or so from the feet of these mountains, there is 

 another break so sudden you can sometimes actually stand with 

 one foot in one belt and the other in the next. The difference is 

 between grass underfoot on the south side and no grass at all 

 on the north side. It is a most surprising phenomenon and looks 

 as if fire had eliminated the grass. Here the subtropical savan- 

 nahs begin. 



TWO HUNDRED MILES OF SAND 



This province may thus be divided into northern and southern 

 portions by the Rio Grande and the much compressed Desert 

 Belt, but it is even more dramatically subdivided the other way 

 —i.e. from east to west— into three parts— a coastal, a central 

 which we have just visited, and an inland area which we will 

 pass through on our way to the next province. The coastal strip 

 is a land unto itself and most fascinating. It varies widely in 

 both appearance and content, and has to be broken down into 

 at least five strips all running parallel to the coast line. First, out 

 to sea, lies a string of sandy islands covered with sea grape and 

 other low, tangled, salt-loving vegetation. Second, about three to 

 five miles offshore is a sandspit. not a mile wide, that stretches 

 all the way from Galveston to Tampico with only occasional 

 breaks opposite the mouths of the larger rivers and where some 

 shipping channels cut through it One stretch of this. Padre 



189 



