722 



JAMES H. GARDNER 



The hiatus between the "Laramie" and the Puerco apparently 

 does not represent so great a time-interval as that between the Torre- 

 jon and the Wasatch. The indications are that the unconformity 

 at the base of the Puerco is in part one of overlap. The angularity 

 is slight between it and the underlying "Laramie" and Lewis shale. 

 However, the direction of strike at the point of overlap is not the 

 same as in the lower formation, which fact probably indicates a 

 slight folding of the Cretaceous rocks and subsequent erosion previous 

 to the deposition of the Puerco formation. On the other hand, the 



ri&lJi 



Fig. 6. — Shale of the Nacimiento group, three miles northeast of Nacimiento, 

 New Mexico. Tilted to vertical by uplift of the Nacimiento Mountains. 



break at the base of the Wasatch is represented by a very strong angular 

 unconformity indicating a long period of erosion previous to its 

 deposition, after the close of the Torrejon. 



The unconformity between the Puerco and Torrejon formations 

 cannot be noted in the field except on fossil evidence. It is highly 

 probable that it is one essentially of overlap with very little strati- 

 graphic break. The two formations are so closely similar in lithologic 

 character that it is difficult to distinguish one from the other without 

 the assistance of fossils. For this reason, the two could not be indi- 

 cated separately in the brief season spent in the preparation of data 

 for the accompanying map. However, the base of the Torrejon is 



