| |
| | AR Geol |
 | | Arkansas is divided into a highland area in the northwest and a lowland region in the south and east. |
 | | The sedimentary deposits of the lowlands are mainly unconsolidated clay, sand, and gravel of Quaternary age, poorly consolidated deposits of clay, sand, silt, limestone, and lignite of Tertiary age, and consolidated (to a limited extent) deposits of Cretaceous marl, chalk, limestone, sand, and gravel (see Geologic Map of Arkansas). |
 | | When most of the sediments that compose the rocks in the highland region of Arkansas were being deposited, north Arkansas was a shallow south-sloping sea floor (continental shelf), the Arkansas River Valley was near the edge of the shelf, and the Ouachita area was a deep abyssal plain (see General Geologic History). |
| www.state.ar.us /agc/argeol.htm (904 words) |
|