430 J). R. Semmes — Tertiary Intrasives. 



stones crumpled between the massive San Andreas lime- 

 stone above and the igneons rock, or even the massive 

 sandstones of the Abo and limestones of the Magalena 

 group which should be found below. This explanation is 

 supported by the fact that the Ye so crumpled series 

 changes gradually through an upper series of slightly 

 folded red shales to the unfolded limestone above. If 

 there was an actual unconformity and accompanying 

 erosion interval one would expect a sharp contact between 

 the two, but such a break cannot be found. Incompetency 

 on such a scale is unusual, possibly unique, but the exist- 

 ing structural conditions are difficult to explain in any 

 other way. 



Age of the Folding in the Roswell Area. — The two dikes 

 east of the Pecos and the sill near Dunlap can be consid- 

 ered, therefore, to be later Eocene or younger in age. It 

 is possible that these intrusions may represent later 

 stages in Tertiary igneous activity, when the basaltic in- 

 trusives and extrusives originated, and may even be 

 derived from some source quite unrelated to intrusives of 

 the Sierra Blanca area, such as a concealed center of 

 igneous activity under the Llano Estacado. In this case 

 the dikes may be of middle or late Tertiary age. 



The age of the folding that has given rise to the peculiar 

 and characteristic sharp, elongated anticlines in the lime- 

 stone area west and southwest of Roswell cannot be defin- 

 itely ascertained, but it is not unreasonable to suppose 

 that at the time of the intrusion of the larger bodies of 

 igneous rock and the crumpling of the Yeso, the stresses 

 that were set up in the overlying limestone were relieved 

 by budding along lines roughly parallel to the trend of 

 these intrusions. The age of the folding in this case would 

 be early Tertiary, though it is quite possible that it may 

 have occurred at a much later date, for there are indica- 

 tions of even Recent movements expressed in the caliche 

 that occurs throughout the area. The determination of 

 the approximate age of this folding should be of interest 

 from the point of view of oil and gas production, for 

 should it be conclusively shown that the folding in this 

 area is of comparatively recent age one might reasonably 

 conclude that relatively little oil would now be entrapped. 



University of Alabama, 

 University, Alabama. 



