THE ORDOVICIAN PERIOD. 



319 



The above section is for Allegany County, 

 lower formations are exposed as follows: 1 



In Washington County, 



Martinsburg. 



Shenandoah 



(The lowest part of 

 this formation is 

 Cambrian.) 



700-1000 

 2500 



Black and gray calcareous and argillaceous 

 shales, fine-grained and uniform. 



Blue and gray limestones and dolomites, with 

 some slates and argillaceous shales. 



Strata much folded. 



Section in Eastern Kentucky. 2 



Names of Formations. 



Thickness 

 in Feet. 



Characteristics. 



a ( (The upper part of this 

 .2 ! formation is Devo- 

 J3 1 nian) 





Brown siliceous limestone at the base; light 





blue clav-shale and coarse yellow sandstone; 





brown limestone, frequently cherty. 



02 I Panola formation 



1-70 





Unconformity. 









r Richmond formation. . 



300 



Blue calcareous shale, with thin beds of lime- 

 stone. 



c 



Garrard sandstone. . . . 



70-100 



Brown, calcareous. 





Winchester limestone. 



200-230 



Thin-bedded, blue, crystalline, with bands of 



> 







calcareous shale. 



o 



Flanagan chert 



0-40 



Thin-bedded, gray limestone and calcareous 



o 







shale; nodules and bands of chert. 



Lexington limestone . . 



140-160 



Thin-bedded, gray; nodules of chert at base. 





Highbridge limestone. 



190 + 



White limestone grading downward into gray 





1 





limestone and calcareous shale. 



Strata nearly horizontal. 



Sections in the interior.— In the interior the sections are likewise 

 variable. 3 The sections of the Ordovician, in the general sections 

 given in the Appendix, give some idea of the range of the system 

 in this region. To these may be added the following: 



1 Clark, Maryland Geol. Surv., Vol. I, pp. 179, 180. 



2 Campbell, Richmond (Ky.) folio, U. S. Geol. Surv. All the formations of this 

 section are classed as Silurian in the folios. 



3 The following folios give detailed sections of the exposed Ordovician between 

 the Appalachians and the Rockies: London and Richmond, Ky.; Columbia, McMinn- 

 ville, Pikeville, Sewanee, and Standing Stone, Tenn.; Atoka, I. T. See also state 

 reports of New York, Ohio, Indiana, Michigan, Illinois, Wisconsin, Minnesota, Iowa, 

 Missouri, Kentucky, Tennessee, and Arkansas. For areas north of the United States, 

 see the geological reports of Canada. 



