366 Branner — Former Extension of the Appalachians 



caused by a depression, the thickness of these sediments should 

 afford some clew to the amount of that depression. The thick- 

 ness of the Cretaceous beds in Arkansas is estimated at 3520 

 feet.* In Texas, near Austin, the Colorado river exposes 52 L0 

 feet of rock overlying the Paleozoic, while further south, the 

 Comanche alone is said to be nearly 5000 feet thick. f The 

 dip of the Tertiary beds of Arkansas suggests a possible thick- 

 ness of more than 3000 feet of Eocene alone in that state.:); 



A bore hole put down on Orange Island, Louisiana, 130 

 miles due west of New Orleans, penetrated 2100 feet of salt 

 and other sediments.§ The age of these salt beds is not 

 known;] they may be either Cretaceous or Tertiary — more 

 likely the former. 



At Galveston, Texas, a deep well penetrates 3070 feet of 

 sediments without reaching the Eocene.^ These facts point to 

 3500 feet of Cretaceous, 3000 feet of Eocene and more than 

 3000 feet of sediments above the Eocene, in all over 9500 feet. 



In western Alabama the Cretaceous beds are 2575 feet thick, 

 while the Tertiary and post-Tertiary are 3120 feet — a total of 

 5705 feet deposited in that region since the Appalachian subsi- 

 dence.** 



Although more or less disconnected, these facts strongly sug- 

 gest a total thickness of Cretaceous and post-Cretaceous sedi- 

 ments of somewhere between 5000 and 10,000 feet in that part 

 of the embayment which the old Appalachian land is believed 

 to have crossed. Such a depression would submerge the entire 

 Appalachian system of to-day. 



It cannot be positively stated, however, that this thickness 

 extends over the entire lower Mississippi area, or even that it 

 occurs at any one place. Indeed it is well known that there 

 are Cretaceous outliers in Louisiana without any Tertiary beds 

 on top of them. ff 



The " sunk lands" — The ancient earthquakes in northeast 

 Arkansas and southeast Missouri were in the upper portion of 

 this embayment. It is well known that at the time of these 

 earthquakes large tracts of land sank and produced lakes, and 



*R. T. Hill, Geol. Surv. Ark., Ann. Rep., 1888, ii, 188. 



fR T. Hill, Amer. Geol., May, 1889, iii, 289; this Journal, vol. cxxxiv, 301. 



% Geol. Surv. Ark., Ann. Rep., 1892, ii, 186. 



§ A. F. Lucas, Eng. and Mining Jour , Nov. 14, 1896, 464. 



I Geology of Lower Louisiana and the salt deposit on Petite Anse Island, by 

 E. W. Hilgard, Smithsonian Contributions to Knowledge. No. 248, Washington, 

 1872. 



^[Dumble and Harris, this Journal, July, 1893, vol. cxlvi, 39-42. 



** E. A. Smith, The Coastal Plain of Alabama, p. 27. In the same volume Dr. 

 Langdon gives a general section of 4215 feet, and the columnar sections (pi. 28 r 

 p. 728) give a maximum of 4175 feet of Cretaceous and Tertiary. 



f f E W. Hilgard, this Journal, vol cii, p. 395 ; Smithsonian Contributions No. 

 248, p. 27; Mineral Resources of the U. S. (1883), p. 557. 



