36 GEOLOGY. 



creek, also, and quite near Eagle Pass, several conspicuous layers are seen. A blacksmith, 

 once connected with the garrison at Fort Duncan, used this coal for some time in his shop ; and 

 having satisfactorily tested its value as an article of trade, went to mining it. There was a 

 ready market at San Antonio ; the cost of the labor, however, in getting it out, together with 

 the great expense of transportation on account of the Indians, put an end to the mining opera- 

 tions of this enterprising individual. 



Small seams of coal appear also on the Mexican side of the river, just below the mouth of the 

 Escondido, which is two and a half miles below Eagle Pass. 



The thickest layers of coal noticed, however, are on the slope of the Lizard hills, below the 

 deserted rancho Palafox ; a more bituminous coal occurs here in layers from 4 to 5 feet thick. 



According to our experience, the finest and best of all the lignite coal in the valley of the 

 Eio Bravo is that which occurs in the neighborhood of Arroyo Sombreretillo. This is apparently 

 the most bituminous observed on the whole line. 



Off from the river, near Santa Kosa, lignite coal was seen. Although its layers are thinner, 

 and. its quality inferior to the various deposits heretofore alluded to, yet its relation to and close 

 connexion with them hardly admits of a doubt. The layers, generally horizontal, are here 

 thrown up almost vertically ; which position is the natural consequence of their being placed 

 near the basaltic dyke frequently referred to before. 



BITUMEN. 



It is but proper to mention here the occurrence of another fossil, not less interesting and 

 valuable than coal. This is a sort of fossil resin or bitumen, which was met with in loose 

 scattered strings on the slope of " White Bluffs," about 20 miles below Eagle Pass. Some few 

 and but small specimens (such as could be saved) were sent to Dr. John Torrey for examination, 

 who found them to be similar to a substance which he had received some time previous from the 

 province of New Brunswick, and examined in order to elucidate a law-suit there pending. Can 

 it be that the occurrence of this fossil in these extreme cretaceous localities proves a close rela- 

 tionship between their respective strata ? 



BLUE OOLITE-LIKE LIMESTONE, 



Other intermittent strata of the upper green sand belt may also be considered as characteristics. 

 For instance, there appears frequently a blue coarsely-grained limestone of a decided oolitic 

 texture, often showing a somewhat crystalline and sharp fracture. This is sometimes alter- 

 nately intersected by and covered with an ochre-colored stratum, usually of a more sandy struc- 

 ture. Both of these rocks abound in fossil shells of a more recent cretaceous, if not of tertiary 

 age. They cannot, for this reason, be pronounced as truly oolitic, however much their struc- 

 ture and appearance might justify such a suj^position. Wherever this limestone occurs, it 

 affords to the inhabitants the material for building their houses, and is also burnt in kilns for 

 domestic use. May it possibly be identical with the " Calcaire grossoir" of the French ? Some 

 strata of this limestone show large masses of a compound, consisting either of magnetic iron 

 combined with sand and marl, or clay, or an aggregation of the latter strongly impregnated 

 with the former. 



