222 'Tertiary. 



grey, or variegated clay. The sand beds are usuall^^ more or less 

 argillaceous ; sometimes but little, or not at all so. Like the Ripley 

 Group, it contains, occasionally, patches, plates, and thin layers of 

 ferruginous, sometimes argillaceous sandstone, and as in that group, 

 presents, locally, massive blocks of sandstone on high points. At 

 La Grange, a fine section of the group, more than a hundred feet in 

 thickness, is exposed. It includes within its outcrop, nearly all of 

 Fayette, Haywood, Madison, Gibson, and Weakley counties ; the 

 larger parts of Hardeman, Carroll, and Henry ; and small parts of 

 Shelby, Tipton, Henderson, Dyer, and Obion. He supposed this 

 group to be of Eocene age, and to have a thickness of about 600 

 feet. This group must not be confounded with the Post-pliocene 

 Orange sand of Hilgard, which occurs in Mississippi and Louisiana. 



The Porter's Creek Group contains proportionally more laminated or 

 slaty clay than the Orange Sand or Lagrange Group. Along the Mem- 

 phis and Charleston railroad, the belt of surface occupied by the 

 group is about eight miles wide. It becomes narrower in its north- 

 ward extension, and appears to be the northern extension of the lower 

 part of Hilgard's Northern Lignitic Group. The thickness is from 

 200 to .300 feet, and in this are usually several beds of slaty clay from 

 five to fift3' feet in thickness. It is well exposed on Porter's creek, in 

 Hardeman county, and on the road from Bolivar to Purdy, commenc- 

 ing about seven miles from the former place, and extending to or be- 

 yond Wade's creek. 



Prof. E. W. Hilgard* described the Grand Gulf Group, Orange 

 Sand and Loess at Port Hudson, Miss., and gave a descending section 

 midway between Port Hudson and Fontania as follows: 1st, Yellow 

 loam, sandy below, 8 to 10 feet. 2d, White and yellow hard pan, 18 

 feet. 3d, Orange and yellow sand, sometimes ferruginous sandstone, 

 irregularly stratified, 8 to 15 feet. 4th, Heavy, greenish or bluish clay, 

 7 feet. 5th, White, indurate silt or hard pan, 18 feet. 6th, Heavy, 

 green clay, with porous, calcareous concretions above, ferruginous ones 

 below; some sticks and impressions of leaves, 30 feet. 7th, Brown 

 muck and white or blue clay with cypress stumps, 3 to 4 feet. 



At the stage of extreme low water the stump stratum is visible to 

 the thickness of 10 feet at its highest point; showing several genera- 

 tions of stumps, one above another, also the remnants of many succes- 

 sive falls of leaves and overflows. The wood is in a good state of 



* Am. Jour. Sci. & Arts, 2d series, vol. xlvii. 



