an infacing slope some in height. Its gently undulating or rolling seaward slope of 2 or 3 ft per mile (500 mm/km), covered with marly strata and rich black soil, determines an important cotton district. Then comes the East Texas timber belt, broad in the northeast, narrowing to a point before reaching the Rio Grande, a low and thoroughly dissected escarpment of sandy Eocene strata. This is followed by the Coast Prairie, a very young plain, with a seaward slope of less than 2 ft per mile (400 mm/km), its smooth surface interrupted only by the still more nearly level flood plains of the shallow, consequent river valleys. Near the Colorado river, the dissected escarpment of the Grand Prairie passes southward changing to a more nearly horizontal structure into the dissected Edwards plateau. The Edwards plateau is referred to later as part of the Great Plains. The plateau terminates in a maturely dissected fault scarp approximately 300 or in height as the northern boundary of the Rio Grande embayment. From the Colorado to the Rio Grande, the Black Prairie, the timber belt and the Coast Prairie merge in a vast plain, little differentiated, overgrown with chaparral (shrub-like trees, often thorny), widening eastward in the Rio Grande delta and extending southward into Mexico. Although the Coast Prairie is a sea bottom of very modern uplift, it appears already to have suffered a slight movement of depression. Its small rivers all enter embayments. However, the larger rivers seem to have counteracted the encroachment of the sea on the land by a sufficiently active delta building with a resulting forward growth of the land into the sea. The Mississippi has already been mentioned as rapidly building forward its digitate delta. The Rio Grande, next in size, has built its delta about forward from the general coastline. Since this river is much smaller than the Mississippi, its delta front is rounded by seashore effects. In front of the Brazos and the Colorado, the largest of the Texan rivers, the coast-line is very gently bowed forward as if by delta growth. The sea touches the mainland in a nearly straight shore line. Nearly all the rest of the coast is fringed by off-shore reefs or barrier islands, built up by waves from the very shallow sea bottom. Due to the weak tides, the barrier islands continue in long unbroken stretches between the few inlets. Habitats