ATTITUDE AND THICKNESS OF THE DEPOSITS. 229 



decisively marine Cretaceous forms and those containing marine Eocene 

 forms. The average dip does not exceed 100 feet per mile, and we saw- 

 nothing in any of the exposures on either hank of the river in this space 

 to indicate a change until we reached Webb bluff itself. The entire 

 appearance of the upper portion of this bluff was so different from that 

 of the materials we had been examining for the three previous days 

 that it was remarked even before we landed. 



The upper Cretaceous Section. — If the estimated dip of 100 feet per 

 mile can be relied on (and no evidence was found in the field work to 

 cast any doubt upon it) the section as given would have a total thick- 

 ness of over eight thousand feet, of which the upper Cretaceous deposits 

 constitute about 7,800 feet, divided as follows : 



Feet. 



' Escondido beds 3,300 



^ , t. t • • Coal series 901 > 



Eagle I ass division - ^ Migud bedg m 



[ Upson clays 700 



Pinto limestones 1 ,500 



Val Verde flags 600 



t 



SI )( i 



It may not lie prudent, however, to rely implicitly upon the apparent 

 dip in such materials as form the Escondido beds, because faulting might 

 occur in places and be entirely unnoticed in such an examination as we 

 could make. It is therefore possible that future work may somewhat 

 reduce the estimate here given. 



REYXOSA BEDS. 



In May, 1880, I observed along the line of the Southern Pacific rail- 

 way between San Antonio and Eagle Pass a deposit usually consisting 

 of a larger or smaller quantity of gravel cemented by a very porous or 

 tufaceous limestone. In some places the gravel seemed to be entirely 

 missing and only the limestone present. The same deposit was noticed 

 north of Eagle Pass on our visit to the coal mines, and we found it 

 forming the summits of the hills at many localities along the river 

 during our voyage from Eagle Pass to Edinburg. The thickness of this 

 deposit as noted was from 3 to 30 feet, and in some instances it was 

 overlain by the yellow silt flanking the Rio Grande. At the town of 

 Reynosa (in the Mexican state of Tamaulipas) and opposite Edinburg 

 in Texas we found a much larger and firmer deposit of limestom — the 

 same indeed which was designated in the report of the Mexican boundary 

 survey Cretaceous limestone. Our examinations resulted in finding 



