SECTIONS OF CRETACEOUS DEPOSITS. 223 



Opposite the extremity of the line of biuffs, on the Mexican side and 

 a short distance above Piedro Pinto creek, the Rio Grande turns abruptly 

 westward, and for a quarter of a mile flows in rapids over the edges of 

 Underlying limestone. It is here that the water is to be taken out for 

 irrigating the valley north of Eagle Pass, which contains about forty 

 thousand acres of irrigable land. The exposures of the limestone con- 

 tinue from here to Las Moras creek, a total distance of 15 miles from 

 its first appearance. The following sections will show its character : 



Cou- Creek Section. 



Feet. 



1. Thick-bedded limestones, with interbeddings of clay shales and nodules 



of altered pyrites 40 



2. Similar limestones in thinner beds 35 or 40 



Fossils. — Inoceramus, Gryphsea, Ammonites, Baculites, of undetermined 

 species ; fossils sometimes ferruginated. 



Texaquito Creek Section. 



1 . Gravel, with calcareous cement (Reynosa beds) 



2. Bowldery limestone containing numerous shells of Exogyra ponderosa, 



Eoemer 6 



.">. Chalky limestone f> 



4. Softer limestones of similar character, with several species of Inoceramus 



and other fossils 6 



5. Yellow bowldery limestone in beds separated by bands of limy clay ; 



the limestone becomes more chalky in appearance toward the base 

 (upper Gryphsea bed, characterized by Gryphsea aucella, Roemer, 

 which is very abundant toward the base, but disappeai"s toward the 



top) 16 



0. Harder limestone, much broken, with shales and limy clays 25 



7. Obscured by later gravel 20 



S. Limy clay, with great numbers of shells of Exogyra costata and Inoa - 



mm us, sp. und 



9. Yellow limy shales, with same fossils as number 8, and containing 



ferruginous seam 4 



in. Clayey limestone, with a large Ammonites (14 inches in diameter). Nau- 

 tilus, sp. now, and immense Inoceramus shells. This limestone is 

 bedded in strata twelve to fourteen inches in thickness and strongly 

 jointed. The compass bearing of join! planes is \". 20° E., and the 

 lines contain oxide of iron. The Inoceramus here, :is elsewhere, i^ 

 preserved in two ways: In one they are simply molds showing the 

 outer form of one ur both shells; in the other, sljell fragments and 

 sometimes entire shells occur. Specimens were measured having a 

 Length of i;> inches 25 



/."* Minns Section. 



1. Gravel, chalky limestone, with some iron pyrites. Inoceramus of several 



species, Nautilus, Ammonites, Baculites, etc., to creek \ 



