while, some miles ahead, the artillery were seen to halt enjoying the luxury of _water_. As the soldiers reached it all discipline was forgotten; their arms were thrown down, and they rushed boldly in, thrusting their heads beneath the waves in their desire to quench the thirst that was consuming their vitals."[98] Such is the natural aspect and character of the desolate region between the Nueces and the Rio Grande,--a chequered wilderness of sand and verdure,--fit only for the wild beasts that inhabit it, and properly described in former days, as a suitable frontier between the great republics of North America. * * * * * On the 21st of March, all our forces concentrated on the Arroyo Colorado,--a salt stream or lagune nearly one hundred yards broad, and so deep as to be scarcely fordable,--situated about thirty miles north of Matamoros. Had the enemy attacked us here his assault would have been formidable, wearied as were our troops with the distressing marches of previous days. Bold, bluff banks, twenty or thirty feet high, hem in the stream, whose borders, on both sides, are lined, for a considerable breadth, with impervious thickets of _chapparal_. These thorny groves are to be found in all sections of the south, varying in size from a few yards to a mile in thickness, so closely interlaced and matted with briers and bushes as to prevent the passage of animals larger than a hare. They are the sorest annoyances of travellers in Mexico, and often force the wayfarer to make a long circuit to pass their limits, though they reward him for his trouble by supplying an abundance of the _tuna_--a luscious fruit of the prickly pear,--which grows luxuriantly on these natural and impenetrable walls. Such, with the barrier of the stream, was the fortification nature had interposed for the safe guard of Mexico at the Arroyo Colorado. But the inert natives seemed indisposed to take advantage of those rare defences, though not without some hostile demonstration which the resolute conduct of Taylor soon overcame.