lOlJf^ Geology of Chapel Hill 29 



Purefoy's mill about two miles south of Chapel Hill. An out- 

 crop occurs also at McCauley's Quarry about seven miles to the 

 west. 



Before the close of the era, great intrusions and uplifts oc- 

 curred tilting the stratified rocks to an angle of 65 degrees. The 

 Chapel Hill stock may have had its origin at this time. It con- 

 sists chiefly of granitoid rocks,^ (granites,^ etc.) but is 

 believed to be in part composed of basic igneous rocks derived 

 by magmatic segregation. It is cut by numerous dikes, both 

 acidic and basic, ranging from granitoid to felsitic textures. The 

 dikes occupy the joint planes which extend approximately N. 

 30 E. and K 60 W. 



PALEOZOIC EKA 



That this region was an area of high land during the earlier 

 part of this era, is shown by the great volumes of sediment 

 derived from it. These are the sedimentary rocks of western 

 North Carolina, eastern Tennessee and Kentucky and have a 

 total thickness of nearly 20,000 feet. This continent, known as 

 Appalachia, sloped to the west or northwest and probably ex- 

 tended eastward into the area now covered by the Atlantic 

 Ocean. The Paleozoic seas covered most of what is now the 

 Mississippi Valley and extended east to the present position of 

 the Blue Ridge Mountains or farther.^ 



ISTear the close of the era, great stresses produced the Ap- 

 palachian Mountains by very slow folding which also affected 

 our area causing a relative uplift in western North Carolina. 

 This changed the slope of the land and our streams flowed east- 

 ward or northeastward over a lower area. 



MESOZOIC ERA 



After the tilting of the surface and the erosion that followed, 

 an incursion of the sea came from the northeast. During this 



3 Eaton. H. N.. Notes on the Petrography of the Granites of Chapel Hill, N. C. 

 Jour. E. Mitchell Sci. Soc. 25 :85. 1909. Also, Flint-Like Slate near Chapel 

 Hill, N. C, ibid 24, 1908. 



* Fry. W. H., Some Plutonic Rocks of Chapel Hill. Jour. E. Mitchell Sci. Soc, 

 27: 124. 1911. 



" Pratt, Dr. J. H., Geology of Western N. C. Jour. E. Mitchell Sci. Soc. 29 : 

 35. 1913. 



