222 E. T. DUMBLE GEOLOGY OF THE RIO GRANDE. 



have described from Anderson county.* In some localities, especially on 

 the Mexican side, the ferruginous coloration appears on the flat surfaces 

 of the flags in beautiful grainings, many specimens of which can he 

 seen in Eagle Pass and Porferio Diaz. The only fossils which I found 

 were different species of InOceramus, except toward the top Avhere a few 

 small ammonites were seen ; but it is possihle that others may he 

 obtained on closer examination. 



A thin seam of lignitic matter was observed in the flags at the mouth 

 of Sycamore creek, on the southern side of the bluffs.f 



The Pi lib) lame-stone. — Sycamore creek flows at the base of the Val 

 Verde bluffs, which at its mouth turn sharply northeastward and, after 

 running hack from the river for several miles, turn southeastward again, 

 and then run back toward the river, leaving a valley along the Texas side 

 some 4 miles or more in width. At the southeastern point of the bluff 

 on Sycamore creek the contact of the Val Verde flags with the base of 

 the overlying chalky limestone is found. The difference in the physical 

 character of the two limestones is very marked. The flags show their 

 laminated character throughout, while the overlying limestone is of 

 earthy texture and without any perceptible lamination. The beds' of 

 the upper limestone vary in thickness from one to three feet or more and 

 are separated by bands of laminated limy shales. The thickness of the 

 overlying limestone at this point is not more than 12 or 15 feet. The 

 fossils observed belong to the genera Tnoceramus and Ammonites. 



These bluffs, in common with all others in this vicinity, are capped 

 with 20 to 30 feet of gravel or chalky conglomerate belonging to the 

 Reynosa beds. 



Crossing the valley we find the bluffs at its southern margin on Pinto 

 creek to he of chalky limestones separated by limy clays in bands from 

 one to two feet in thickness, the whole exposure being about 30 feet in 

 height. The only peculiarity noticed was numerous grooves cut in the 

 limestone, extending diagonally across the present creek bed and very 

 nearly in the general direction of the flow of the Rio Grande, 



On the Mexican side of the river, between these two points, a long 

 line of bluffs appears, showing the limestone resting on the flags with 

 apparently a slight difference in dip between them, the dip of the flags 

 being seemingly somewhat greater than that of the overlying limestone. 

 At the southern extremity of this line of bluffs the limestone is in 

 heavier beds (three feet or over) and rises to a height of 40 feet or more 

 above the river. Some cavities of considerable size have been weathered 

 in it. 



*2d Ann. Rep. Geol. Surv. of Texas, 1890, p. 305. 



■(•Mr. Owen informs me that these flags attain a very much greater thickness toward the south- 

 west in Mexico. 



