THE NEW MADRID EARTHQUAKE 53 



Crowley's ridge on the west, and the bluffs on the east side of the 

 valley, while sand and alluvium cover the area under discussion. 

 Beneath the loess is from 6 to 40 feet of Lafayette gravel, followed by 

 a layer of impervious blue clay — the La Grange formation, which 

 varies greatly in thickness, and averages from 100 to 225 feet. Under 

 this impervious blue clay is from 10 to 40 feet of Orange sand, and 

 below this is found the great water-bearing sand, the Silicious Clai- 

 borne, or the La Grange sand of the La Grange formation of Hil- 

 gard, which varies in thickness from 600 to 800 feet. This deposit 

 of sand, which is finer in texture above and below than in the middle, 

 and which is intercalated with thin beds of clay and a considerable 

 amount of lignite, is a reservoir in which the waters from the Tennes- 

 see Mountains and the Ozarks meet under great pressure. Beneath 

 this sand is found from 200 to 300 feet of Porter's Creek (Safford), 

 or Meridian, formation, and under the last is about 250 feet of Ripley 

 sands, another water-bearing formation, the source of the artesian 

 waters of Jackson, Miss., while still lower is the Rotten limestone 

 overlying the Coffee sands, which, in turn, rest unconformably upon 

 the Sub- Carboniferous. 



Numerous drill-wells through and around the sunken district 

 develop the fact that the wells of the region do not flow, but that the 

 water rises to or very near the surface, while those on the border 

 of this district are mainly artesian, or flowing, wells. Starting at 

 Memphis, where there are 140 flowing wells, and going northward 

 along the border of the district, a flowing well 628 feet deep is 

 encountered at Dyersburg, Tenn. ; one 840 feet, at Hickman, Ky. ; 

 one 930 feet, at Wystaff, Ky. ; several over 800 feet, at Cairo, 111.; 

 one 626 feet, at Mound City, 111.; one 710 feet, at the mouth of Cash 

 Creek, 111.; one 62 feet, at Pocahontas, Mo., north of Cape Girar- 

 deau; one 900 feet, at Campbell, Mo.; and one 480 feet, at Parkin, 

 Ark., west of Memphis. 



In the sunken area which is encircled by these flowing wells there 

 are non-flowing wells at Terrell, Ark., 860 feet; north of Memphis, 

 800 feet deep; at Deckerville, Ark., 700 feet; at Caruthersville, 

 Mo., 428 feet; at New Madrid, Mo., 200 feet; and at Sikeston, 

 Kennett, and Marked Tree, Mo. The waters in the flowing well 

 at Cairo are probably derived from the St. Peter's sandstone. 



