FORMATIONS OF THE NACIMIENTO GROUP 717 



The character of individual strata composing the two formations 

 of the Nacimiento group may be gathered from the following section 

 along the west side of the Puerco River below Nacimiento: 



SECTION OF NACIMIENTO GROUP ALONG PUERCO RIVER 

 SOUTH AND WEST OF NACIMIENTO 



(Wasatch formation) 



/TT r -i \ Thickness 



(Unconformity) in peei 



Shale, variegated 20 



Sandstone, brown 3 



Shale, gray 15 



Sandstone, gray 3 



. , Shale, gray and soft sandstone 40 



•^ ^ Sandstone, massive, tan-colored 15 



Shale, yellowish ' 15 



Sandstone, massive, soft, coarse, tan-colored 120 



Shale, gray 20 



Sandstone, massive, soft, tan-colored 30 



(Unconformity) Thickness of Torrejon formation 276 



Shale and soft sandstone 30 



Shale, dark, carbonaceous 10 



Shale, gray 10 



Sandstone, massive, yellowish, lenticular 10 



Shale, variegated 25 



Shale, dark carbonaceous 4 



Puerco ^ Shale, chiefly yellowish 80 



Sandstone, massive, brown, lenticular 10 



Shale, variegated and soft, gray sandstone 200 



Sandstone, massive, coarse-grained, brown 40 



Shale, gray and soft sandstone 45 



Shale, very dark, local coal streaks 4 



\ Shale and soft sandstone of gray and tan colors 90 



(Unconformity) Thickness of Puerco formation 558 



(Lewis shale) Thickness of Nacimiento group 834 



The section given above may be taken as typical for the beds of 

 the Nacimiento group in the type-locality. The total thickness of 

 either the Puerco or Torrejon is variable owing to the unconformities 

 that limit each of these formations at the top. This limitation in 

 thickness is brought about by erosion and removal of rocks during 

 the time-interval after the close of each formation. 



