THE LOWER RIO BRAVO. 45 



to some few members of the Mimosa family, of which latter the Huisache maintains its place 

 nearly down to the tidal sand-hanks of the gulf. 



Lagoons, old river beds, ponds, swamps, pools, hayous, and other similar phenomena now 

 constitute the lowest belt. Here the deceptive mirage constantly bounds the distant horizon, 

 and the scenery, under its influence, presents to the mind but a chaotic dream still hovering 

 over the land — a twilight gift of creation. 



Besides the regularly occurring ebb and flow of the tide, which was observed at Kaneho 

 Lomita varying from about four to six inches, the fauna of the water indicate that the maritime 

 belt has its upper limits in this vicinity. Some little distance below Lomita a two-valved shell 

 and a decapoda, the camaron of the Mexicans, announce the proximity of the sea. Both of 

 these animal forms seem to go up as high through the alluvial deposit as the tide affects the 

 river. 



ALLUVIAL DEVELOPMENT. 



There is another portion of this lowest and most recent formation which, still under the con- 

 tinual action of both salt and fresh water, might be considered only as a rudimentary develop- 

 ment of the alluvial belt along the coast. Not having yet risen above the level of the water, 

 it is called, in the language of the sailors and pilots, the "bar." Such a place aff'ords a home 

 only for the various marine crustacese, and the meeting ground of the sea^owls, the-wreckers of 

 the population of the air. 



In regard to the topographical features of the coast, it may be completely characterized 

 by the statement that it consists partly of the fragments of the solid parts of marine ani- 

 mals, partly of entire or decomposed vegetable forms, partly of deposits of inorganic matter, and 

 partly also of fragments of animals, vegetable matter, and other material brought down by the 

 river. Washed off and brought back again by the varied motions of the waves — sometimes 

 united, sometimes antagonistic — as a matter of course this adjunct of the colluvial belt is always 

 undergoing a change. This is, however, strictly regulated by the varying amount of power 

 exercised on the one hand by the irresistible waves, and on the other hand at times by the no 

 less forcible flood of fresh water. Agents of the sea are atmospheric currents and ebb and flow 

 of tide ; antagonistic to these oscillatory movements are the forces of the river, influenced by 

 the hygrometric conditions of the air and the hyetographic state of the seasons in the country 

 above and along the river. 



The bar, though a mere toy under the action of the forces just mentioned, is not to be over- 

 looked, for it is a constantly increasing piece of land not yet left by the working hand of creating 

 nature, and therefore a matter for observation of much interest. 



The muddy sheet of river water covers the whole view seaward before its mouth, when there 

 is not any wind or current setting against the natural flow of fresh water ; but if south or north 

 winds are prevailing, the muddy tribute of the Rio Bravo, instead of spreading out into the open 

 sea, and commingling there undisturbed with the salt waters, is checked and pressed aside as a 

 long narrow strip along the beach in the direction that the wind sets the current. 



Considering these circumstances, it is therefore clear that the place of deposits, both of the 

 sea and river, gathering about the mouth are kept in a continual and also somewhat regular 

 motion. 



