LOCAL SiLICiFICATlOX OF THE MYRTLE FORMATION 393 



veined more or less abimdanth' with small stringers of quartz. The 

 abundance of fossils and the calcareous cement derived from them has in 

 a measure restricted the circulation of the siliceous solutions to the por- 

 tions poor in fossils, where the quartz veins in consequence are most com- 

 mon. Barely the shells are replaced by pyrite. 



CALCAREOUS CEMENT ASD QUARTZ VEIXS IX THE DOTHAX 



In the northwest portion of the Eiddles quadrangle, a few miles from 

 the end of the Dillard area, and separated from it by a mass of green- 

 stone, the Thomf)Son Creek body of Dothan rocks occurs and contains 

 characteristic specimens of Aucella erringtoni. As in the Dillard area, 

 M'herever the fossils are abundant the cement and veins are calcareous, 

 biit elsewhere they are siliceous. The Dothan rocks on Thompson creek 

 are in most places not silicified or permeated by quartz veinlets any more 

 than the Knoxville rocks of the Dillard area. Generally, however, other 

 portions of the Dothan, where not fossiliferous, are more firmly silicified 

 and abundantly quartz-veined than the rocks of the Dillard area. 



AGE OF THE ROCKS 



That the rocks of the Dillard area are Knoxville is indicated by the 

 wide distribution of characteristic fossils, especially Aucella piochii and 

 Aucella crassicollis. As indicated in the accompanying figure, they have 

 been found at many points throughout the area. A sketch of the Dillard 

 area was published in the American Joiirnal of Science for June, 1907, 

 page 416, but since then, in completing the Eiddles quadrangle, the num- 

 ber of fossiliferous localities has been greatly extended, especially in the 

 southwest portion and along the river above Dillard (figure 4), wliere 

 well preserved forms occur in calcareous pebbles or concretions of an in- 

 teresting conglomerate.'' 



If these fossiliferous nodules are pebbles derived from an aucella- 

 bearing limestone, they would furnish evidence of a limestone character- 

 ized by Aucella crassicollis older than the rocks of the Dillard area, for 

 the conglomerate in question is well exposed by the river and evidently 

 interstratified with the rocks in the immediate vicinity of Dillard. Sim- 

 ilar conglomerate with fossiliferous limestone nodules occurs on tlie river 

 at the mouth of Eice creek. The adjacent sandstones at 1)oth localities 

 contain calcareous concretions, and it is believed that the fossiliferous 

 nodules also may be concretionary and of the same age in general as the 

 rocks of the Dillard area to which the fossils correspond. 



The best examples perhaps of Aucella crassicollis found this year 



° Tlie total number of distinct localities at which Knoxville forms of Aucella have been 

 found in the Dillard area is sixtv-four. 



