S8' INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



tions, but the latter are always found to contain more or less abundant traces of life. In the 

 absence of fossril evidence their age can not be definitely determined, but on structural evidence, 

 obtained chiefly in Tennessee, they are believed to be Lower Cambrian with possibly some 

 pre-Cambrian. 



The rocks of the Ocoee series generally show an increasing degree of metamorphism toward 

 the southeast; and within a few miles of this region they pass into schists and gneisses, the 

 original form of which, whether igneous or sedimentary, can not be readily determined. This 

 iacreased metamorphism toward the southeast is due in part to the greater compression which 

 that region has suffered, and in part to the presence of considerable bodies of various igneous 

 rocks which have been intruded into the sedimentary beds. These intrusive rocks present 

 considerable variety in composition, varying from extremely basic diabase to acid granites. 

 The most common variety is a diorite, which was among the earlier intrusions, and has been 

 subsequently converted for the most part into amphibolite schist. Two belts of this basic 

 schist pass across the southeastern comer of the district. Its southeastern comer is occupied 

 by the Acworth gneiss, which, like the Corbin granite, is probably Archean in age, and formed 

 the foundation on which the oldest sediments of the region were deposited. 



Among these probably pre-Cambrian schists occur some strata which, though 

 highly metamorphosed, are of late Paleozoic age. Thus E. A. Smith records the 

 discovery of plant remains near Mosely, Clay County, Ala., in " semicrystalline 

 (sericite) slates of the Ocoee type * * * at the eastern base of the main range 

 of the Talladega Mountains * * * 8 miles or more from the contact of the 

 'Ocoee' with the unaltered Cambrian of the valley." David White ^^^ reported 

 on the plants as follows : 



Your specimens represent several fragments of large cones in which the axes, the basal, 

 sporangiferous portions of the spirally arranged bracts, the rhomboidal compressed sporangia, 

 and the megaspores are well defined. Precise identification of the material is deferred pending 

 the study of thin sections and the determination of certain points regarding the sporangial walls 

 and their attachment to the basal portions of the bracts. It is clear, however, that we have 

 here fragments of cones whose superficial features appear to represent the common Lepidostrobus 

 type of the upper Paleozoic. Beds containing lepidophytic remains of this type can hardly 

 be older than Devonian at earliest, and should not antedate the Middle Devonian. 



The general proportions and aspect of the cones are suggestive of some of the Carboniferous 

 forms. Although the internal structure of the strobili may be found to indicate a more highly 

 organized genus than Lepidostrobus, we may rest assured that the material is not older than the 

 upper Paleozoic lepidophj'tes. 



I-J 12. GKAND CANYON, ARIZONA. 



The Tonto group comprises a sandstone at the base and shales and limestones 

 above. Walcott^^^ gives the following section: 



The Tonto section at the head of Nunkoweap Valley is as follows, from top downward: 



Feet. 



1. Massive mottled limestone 60 



Fossils: Lingulepis and Ptychopai-ia. 



2. Evenly bedded yellowish sandstone 05 



3. Mottled and variegated calcareo-arenaceous rocks 34O 



4. Thin-bedded sandstones '. 325 



Fossils (near base) : Lingulella, Acrothele, Iphidea ornatella, Hyolithes, Leperditia (three 

 species), Dilichometopus, Olenoides, and Ptychopajria. 



5. Fine-grained passing into coarse reddish -brown sandstone in layers 300 



1,050 



