CHAPTER I. 



GENERAL GEOLOGICAL FEATURES OF THE COUNTRY. 



Washington, D. C, April 1, 1854. 

 Colonel W. H. Emory, United States Commissioner : 



Sir : In completion of the duties assigned me as botanist and geologist to the United States 

 boundary commission, I present the following : 



I. GENERAL PHYSICAL AND GEOLOGICAL FEATURES OF THE COUNTRY. 



The general features of the Mexican Gulf Coast, in connexion with the United States and 

 Mexican boundary line, present a marked contrast with those observed on the opposite Pacific 

 coast. Thus, instead of the high cliffs, abrupt headlands, and general bold and rugged outline 

 exhibited on the Californian coast, the Texan shore-line, throughout its whole extent, presents 

 a uniform, low dead level. Generally, indeed, the main coast is shut in from the open sea by 

 ranges of sand islands formed by the waves of silted sea sand and comminuted shells. Inside of 

 this line of islands shallow bays spread themselves into the indented coast, and here the nume- 

 rous rivers flowing from the interior meet the tide-water. The tide range is moreover small, 

 and thus the alternating differences of level do not favor the formation of navigable estuaries by 

 which the main land may be approached. These features, collectively, give to this coast an 

 inaccessible character, and serve to render its navigation both difficult and dangerous. 



Its rivers are unapproachable, except by vessels of very light draught ; while the inlets to 

 its shallow bays, obstructed by variable sand-bars, present obstacles to navigation, sufficiently 

 proved by the numerous wrecks that strew their beach. Proceeding inland from the line of 

 sandy beach, a gentle slope spreads out in a uniform gradually rising plane, composed of dark 

 rich loam, and covered with luxuriant pasturage. The scenery is rarely relieved of its blank 

 outline by a clump of live oak trees surrounding a sunken morass. Farther on, at a variable 

 distance of 10 to 20 miles, the surface of the ground shows gentle swells, still maintaining 

 its fertile character, and displaying here and there groves of post oak and other timber. The 

 river bottoms adjoining are occupied with a heavy timber growth, principally of elm, {ulmus 

 crassi/olia,) festooned with Spanish moss. The undergrowth comprises a complete maze of 

 shrubbery, matted and tangled together by vines and creepers, and supporting a rank annual 

 growth. 



At a distance of 50 to 80 miles from the coast, the ground-swells become more abrupt and 



form distinct ridges, between which are collected the drainage of the country. Along the course 



of the numerous streams there is an exposure of the geological substratum, consisting first of 



loose gravelly strata, which contain erratic pebbles of siliceous or calcareous character ; to this 



1 M 



