THE TIMBER BELT OR SABINE RIVER-BEDS. 41 



a similar formation to that in which the Ammonites above referred to were 

 found. Large blocks of limestone, with flat and bedded slabs of gray sand- 

 stone, are seen, and many fossils similar to those seen above. A quarter of a 

 mile below this, on the Texas side, is a bluff sixty feet high, composed of beds 

 of friable sandstone, hard shell limestone, with great numbers of oysters, and 

 softer sand and sandy clay strata. The shell rock is in places entirely com- 

 posed of fossils. From here to a point five miles below Las Cuevas Creek, 

 in Maverick County, are found a great number of bluffs, showing a similar 

 formation of sands and clays. The bluffs rise from ten to a hundred feet 

 above the level of the river. They are capped by pebble beds one to five 

 feet thick, which in turn are sometimes covered by five to fifteen feet of gray 

 river silt, containing recent land shells. The pebbles are composed of lime- 

 stone, flint, quartz, chalcedony, agate, black obsidian, jasper, and red pitch- 

 stone. The sandstones vary from a friable rock to a quartzite, and often lay- 

 ers of hard shell limestone or beds of oysters two to four feet thick occur; 

 also, many Upper Cretaceous Ammonites are found in various places. Islands 

 are of common occurrence, and are composed either of river silt or of the 

 older strata. All the bluffs dip horizontally, or from one to three degrees to 

 the southeast. 



At a point five miles below Las Cuevas Creek are the Angostora Rapids. 

 These are caused by a reef of oyster shells, of the same kind as mentioned 

 above, which run across the river, and are covered on either bank by the 

 same gray or buff sandstones. For sixteen miles below here, by river, we 

 find almost uninterrupted outciops of similar deposits of dessicated and in- 

 durated sands and clays, containing many Ammonites and other forms similar 

 to those found at the Cretaceous exposure in Anderson County (pp. 33-34). 

 At this point we come to what is known as Las Isletas. The river is a half 

 mile wide and very shallow. It is full of small islands, consisting of sand 

 bars, and covered by mesquite and cane. The bottom of the river is rocky, 

 and causes almost continuous rapids for five miles. 



For twelve miles below Las Isletas, and to a point three miles below the 

 north line of Webb County, we see many outcrops of a formation similar to 

 those already described, and with similar fossils. But here the fauna changes, 

 and the character of the strata becomes more glauconiferous. The following 

 section shows the character of the bluff at this point: 



WEBB BLUFF. 



1. "White indurated fine sandy clay, with dark streaks, and specks of lignitic matter . 30 feet. 



2. Greensand marl, with many Tertiary fossils, nodules of carbonate of lime con- 



taining glauconite specks 1-8 feet. 



3. Stiff plastic bluish-black clay, jointed, specks of mica 10 feet. 



Dip of strata 3 degrees southeast. 



