Eastern and Southern United States. 469 



Along this section can be seen nearly every known horizon 

 of the American Cretaceous east of the Sierras, except the 

 Laramie (if this is Cretaceous), and even this can be seen along 

 the Rio Grande in Southern Texas, as shown by White, but it 

 is emphatically missing north of that region. This section, 

 when completed, will be the typical one of the North Ameri- 

 can Cretaceous, and will be a standard of criticism and compar- 

 ison for the rest of our country, for it is the area where the 

 formations of the east meet those of the west and where they 

 can be compared side by side. It comprises the thicknesses 

 and details of both the upper and lower formations.* These 

 beds constitute two continuous periods of sedimentation sepa- 

 rated by an unconformity during which there was a great land 

 epoch. 



What is known of them up to date, as recently published, 

 may be summarized as follows : 



Appropriate local names are added as far as can at present 

 be given for the two formations and their subdivisions : 



The Upper, or Black Prairie Formation (Gulp Series). 



{Black Prairie and Lower Cross Timbers Formation.) 



Thickness. 



5. Uppermost, arenaceous (glauconitic) beds. Cretaceous 

 spots of Anderson county, along eastern margin of 

 Cretaceous area in Texas. Rarely found. Has 

 greatest development in Arkansas, as at Arkadelphia + 300* 



4. Marly clay beds. (E. Ponder osa marls.) Main, or 

 eastern area of the Black Waxy region, as seen in 

 parts of Lamar, Fannin, Grayson, Collin. Dallas, 

 Ellis, Nevarro, Falls, McLennan, Williamson, east- 

 ern Travis, Hays, Comal and Bexar counties and 

 Arkansas (" Fort Pierre ") +1 200 



3. The Austin-Dallas Chalk, occurring in a- very narrow 

 strip immediately westward or interior of the above 

 Sherman, McKinney, Waco, Austin (except 6th 

 ward), and San Antonio are situated on this line. 

 Also at Rocky Comfort, Arkansas, "Mobrara" + 600 



2. The Eagle Ford Prairies, or " Fish Beds," immediately 

 west of the foregoing, and composing the Black 

 " hog wallow" prairie of Alvarado, Hillsboro, and 

 the 6th ward of Austin (" Benton ") + 300 f 



1. The'Lower Cross Timber sand, which is the base of 

 this formation north of the Brazos. No. 2 is the 

 base south of that river ("Dakota") + 300 f 



* The word " formation " is here used to signify the structural product of a 

 single, uninterrupted geological event. 



Am. Jour. Sci. — Third Series, Vol. XXXVIII, No. 228. — Dec, 1889. 

 B0 



