278 C. H. Hitchcock — Crystalline Rocks of Alabama. 



Art. XXXVL— The Crystalline Rocks of Alabama ; by C. H. 

 Hitchcock, Hanover, N. H. 



In March and April, 1885, at the request of Professor E. A. 

 Smith, State Geologist of Alabama, 1 studied the crystalline 

 rocks of Eastern Alabama, and was thus enabled to compare 

 them with the similar exposures in Virginia and New England. 

 This region of exploration lies between the Coosa river and the 

 east line of the State. It is the southern end of the long 

 belt of crystalline rocks continuous from New Brunswick and 

 seen farther east in Newfoundland. This area, as is well 

 known, contains three groups of mountains, termed the northern, 

 middle and southern sections. Viewed literally the western 

 border is the most strongly marked, constituting the Green 

 Mountains in New England, the Highlands in New York and 

 New Jersey, and the Blue Ridge in Virginia. The more 

 eastern portion rises to greater altitudes in the White Moun- 

 tains of New Hampshire and the Black Mountains of North 

 Carolina, while the depression between them is equally conspic- 

 uous and profound. The Alabama area lies wholly upon the 

 southern slope of the last section, it being higher near the pas- 

 sage of the Georgia line by the Coosa river than about Auburn 

 and Columbus. The country seems like an ancient table land 

 worn to shallow depths by the tributary streams. 



The geographical area to the west of this crystalline district 

 is marked off definitely by that remarkable boundary, known 

 as the Great Appalachian Lower Silurian Limestone valley, 

 continuous from the Gulf of St. Lawrence to Eastern Tennessee 

 and Northern Alabama. The contrasts on both sides of this 

 boundary are well marked. On the east are the crystalline 

 rocks, folded, inverted, faulted, traversed by igneous intrusions 

 of the whole pre-Tertiary family of eruptives ; on the west all 

 the rocks are fragmental, posed in graceful folds or split by 

 gigantic faults and are very rarely penetrated by unstratified 

 rocks ; on the east the rocks are principally Archasan ; on the 

 west they are Paleozoic ; on the east the ranges are commonly 

 short, with obtusely pointed summits ; on the west the ranges 

 are long barrows passing into plateaus. The eastern are the 

 Alps and the western the Jura of America. It is this Ameri- 

 can Alpine section or the " Atlantic Primary Chain " of 

 Featherstonhaugh which crowds the Coosa River in Alabama. 



The geology of this region in Alabama may be best under- 

 stood by a sketch of the order and position of the strata in a 

 northwest-southeast section crossing them, say from Talladega 

 to Columbus, Ga. 



In Talladega the ubiquitous number II of Rogers — the 



