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Willman, H. B., and John C. Frye, 1970, Pleistocene Stratigraphy of Illinois: Illinois State Geological Survey Bulletin 94, 204 p.

H. B. Willman and John C. Frye

Mounds Gravel (Willman and Frye 1970).

It is named for Mounds, Pulaski County, part of which is on a ridge underlain by the Mounds Gravel.

The deposits included in the Mounds Gravel have previously been called Orange Sand, Lafayette Gravel, Lafayette-type Gravel, Tertiary, Plio-Pleistocene, Continental Deposits, and other names (Amos, 1967; Finch, 1966; Fisk, 1944, 1949; Horberg, 1950a; Leighton and Willman, 1949; Olive, 1966; Potter, 1955a, 1955b; Pryor and Ross, 1962; Ross, 1964; Salisbury, 1891a; Salisbury, ''in'' Stuart Weller et al., 1920; J. M. Weller, 1940). ===History&#47;background=== ==Type section== ===Type location=== The type section is an exposure in a gravel pit 3 miles west of Mounds, SW SW SW Sec. 7, T. 16 S., R. 1 W., Pulaski County, described as the Cache Section (table 6). The Mounds Gravel is classified as a formation. <center> '''Table 6 -- Stratigraphic Sections (partial)'''<br> The following 21 stratigraphic sections describe exposures in Illinois and illustrate many of the aspects of Pleistocene stratigraphy. These sections contain the type localities for 21 rock-stratigraphic units, 4 soil-stratigraphic units, and 3 time-stratigraphic units and include paratypes for several other units. The sample numbers preceded by "P" are the numbers used in the Illinois State Geological Survey collections. Analytical data on many of these samples are on file at the Survey. The sections are arranged alphabetically by name. <gallery caption="" widths=250px heights=250px perrow=4> File:94-tb_6-a.jpg|alt=Stratigraphic table showing sections and sample data for Pleistocene units in Illinois, including type localities and representative exposures.|{{File:94-tb_6-a.jpg}} </gallery> </center> ===Type author&#40;s&#41;=== ===Type status=== ==Reference section== ===Reference location=== ===Reference author&#40;s&#41;=== ===Reference status=== ==Stratigraphic relationships== In southern Illinois the Mounds Gravel has commonly been related to three terrace surfaces-- the upper, called Karbers Ridge, Ozark, Calhoun, Lancaster, or Williana, at an elevation of 580 to 620 feet; the middle, called McFarlan, Central Illinois, Bentley, or Smithland, at 450 to 500 feet; and a lower terrace, called Elizabethtown, Montgomery, or Havana, at 380 to 400 feet. In addition, gravel similar in composition occurs locally at the level of the Ohio River-- for instance, at Ft. Massac State Park at Metropolis, Massac County, at an elevation of about 300 feet. The gravel at all these levels is almost identical in character, except for local differences in coarseness. The validity of the terraces as separate erosional benches, capped by gravel generally less than 20 feet thick, is open to question. The middle and upper terraces may be part of a single alluvial fan (Potter, 1955a); in places the benches may be erosional on the gravel; and in other places the apparent relief may be the result of post-gravel warping. ==Extent and thickness== Although the Mounds Gravel is nearly continuous in the area south of the Cache Valley, it is represented only by scattered pebbles north of the valley, except in the upland bordering the Mississippi Valley south of Thebes (Pryor and Ross, 1962). Similar gravel also has been observed on top of the Shawneetown Hills (Butts, 1925). ==Lithology== The Mounds Gravel consists of the brown chert gravel and associated red sand that occur south of the Shawnee Hills of southern Illinois. <br> The gravel is composed dominantly of medium to dark brown chert pebbles, most of which are considerably rounded, and some even well rounded. Completely angular pebbles are scarce. Well rounded quartz pebbles, most of them less than half an inch in diameter, are abundant. The lithology and mineral composition of the deposits has been described in detail elsewhere (Lamar and Reynolds, 1951; Potter, 1955a).<br> The Mounds Gravel is derived largely from the Tennessee Valley. However, the gravel near the Mississippi Valley west of the Cache Valley and south of Thebes contains the purple quartzite, jasper, and agate that occur in the Grover Gravel and were derived from the Precambrian rocks of the Lake Superior region. The Mounds Gravel contains much higher percentages of kyanite and staurolite than the Grover Gravel, and its chert pebbles are darker brown and more polished. ==Core&#40;s&#41;== ==Photograph&#40;s&#41;== ==Contacts== ==Well log characteristics== ==Fossils== ==Age and correlation== ... (unchanged)

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