74 RICHARDSON: DIFFUSION IN OIL-FIELD WATERS 



which the samples were taken are about 40 miles apart, and 

 the water-bearing horizons, of Devonian age, are separated 

 stratigraphically about 4500 feet. 



The history of deep-seated waters of this kind is a subject 

 of debate. In a recent number of Economic Geology I have 

 suggested, as a working hypothesis, that the Appalachian oil- 

 field brines are a mixture of waters originally occluded with the 

 sediments when deposited and of meteoric waters of later origin 

 which have entered the rocks during periods when the region 

 was above sea level ; that these waters have leached great masses 

 of sedimentary beds containing disseminated salt, and that 

 they have undergone a series of changes in composition, the 

 saline matter tending to accumulate because of the slow circu- 

 lation dependent on the synclinal structure of the region. 

 Among other causes of the sodium chloride content of the 

 waters and of the increase of concentration with depth, I sug- 

 gest that diffusion from beds of rock salt may be an impor- 

 tant factor. Such beds in the Salina formation are known to 

 underlie at least part of the Appalachian oil-fields. Thick 

 deposits of rock salt actually occur 600 feet below the horizon 

 in the well from which the water of sample B was obtained, 

 and others may occur. 



It is worthy of consideration that beds of shale, especially 

 connecting lenses of sandy shale, separating the more porous 

 beds of sandstone in the Appalachian oil-field section may be 

 porous to such an extent that there exists a continuous, though 

 very irregular, network of minute pore spaces connecting the 

 beds of rock salt with the overlying beds in which salt water 

 is found. The deep-seated waters are under great artesian 

 pressure, as shown by the fact that in the well from which 

 the sample represented by analysis B was obtained the water 

 was forced 4000 feet above the horizon where it was encoun- 

 tered in drilling. Such pressure tends to fill with water the 

 pores even of very fine-grained strata, and it seems plausible 

 that in the rocks of the Appalachian oil-fields there are con- 

 tinuous pore spaces occupied by water. If such conditions 

 exist, diffusion must act. 



