The Knobs region in its typical development is a narrow belt of country surrounding the Blue Grass, characterized by the presence of conical knobs, which are erosion remnants of the upland behind Muldraugh's Hill on the west and south, and the Pottsville Escarpment on the east. The region of the dissected border of these uplands is commonly included in the Knobs until a definite upland has been attained. In their characteristic development they rise from the level of the Lexington plain. Similar knob-like erosion remnants, which front the other escarpments in the state, have not received recognition as distinct physiographic units. Geologically it is the region of the Ohio-Waverly outcrop—the shale country between the limestone country of the Blue Grass and the bordering Pennyroyal and Cumberland Plateaus. Where the Silurian-Mid-Devonian section is mainly limestone the region is included in the Blue Grass. Where largely shale, as east of the Arch, it is allied with the Knobs.
|FIGS. 1,2. Diagrams illustrating the
formation of Knobs (Pauline Young).
FIG. 1 (left). Muldraugh's Hill (or Pottsville Escarpment)
with portions of the upland partly
|FIG. 3. View of the Blue Grass region from
Hall's Gap south of Stanford (Caufield
and Shook). Hall's Gap is a notch in Muldraugh's Hill and the flat lowland of the Blue
Grass is the Lexington peneplain.
A number of regional types are recognized :
(a) The border zone of the encircling highlands characterized by its conical knobs (erosion remnants) which become higher, more numerous, and flat-topped as the escarpments behind are approached, and rise above the level of the Lexington plain. This is the typical Knobs country. The Knobs are carved mainly from the Ohio and Waverly (New Providence-Keokuk) and with the soft shales below is a region of steep slopes and rapid erosion and soil wash. Near the larger drainage lines broad shale-floored valleys are developed. Conical forms are normal, remaining flat-topped only where remnants of the original cap rock are preserved.
(b) The Lexington peneplain is not coextensive with the outcrop of the Ordovician and the Blue Grass, but has been extended into the area of Ohio and Waverly outcrop, particularly along major streams as the Ohio River in Lewis County. Similarly, it has been extended far into the Mississippian in the Louisville region. Here, there must be recognized a section of the Knobs whose summit level is an extension of the Blue Grass level. It is a typical knobs country, but one in which the hills are erosion remnants of the Lexington plain.
(c) The general area of outcrop of the Louisville and Jeffersonville limestones is essentially Blue Grass in character (see p. 172). In contrast, in the eastern area of outcrop the Silurian (Crab Orchard) is largely shale and gives rise to a country more like that of the Knobs. In essentially this same area (eastern Clark and Madison counties for example) much of the Richmond is shale, which gullies rapidly and gives a similar result.
|FIG. 1. Looking up (north) the
Ohio River from Alum Rock at Vanceburg,
Lewis County. The plateau level into which the Ohio River valley is
trenched lies just behind (east of) the Waverly Escarpment and is the
upland surface of that cuesta.
|FIG. 2. Knobs region of Estill County.|
|FIG. 3. Joe Lick
Knob, 4 miles northeast of Berea with Muldraugh's Hill in
the background. The knob is composed of the Ohio and Waverly shales
preserved in a graben. In origin it is thus much like Burdett Knob (p. 148)
but is much closer to Muldraugh's Hill.
|FIG. 4. Kenwood Hill, a knob a
few miles south of Louisville. It rises
above the Scottsburg lowland to about 750 feet, coming close to the
Lexington peneplain level. The knobs of the usual Knobs region rise
from the Lexington plain level to that of the Pennyroyal and
The Knobs is an area of inferior soil, particularly that derived from the Ohio (Chattanooga) shale. The steeper slopes of the Knobs and the soft and relatively impervious character of the bedrock lend themselves to rapid erosion and such areas under cultivation soon go to pieces. In the flat lowlands the tight clay soils drain poorly. When drained and fertilized they are productive. The alluvial bottoms are better, as soils from external sources are mixed with those of local origin.
Springdale topographic sheet (± x ⅓)
The area thus includes:
(a) An eastern belt in front of the Pottsville Escarpment with its Rockcastle conglomerate cap, flat-topped while the cap remains, conical after its removal.
(b) The southern and western belt in front of Muldraugh's Hill, where the St. Louis forms the cap rock. These are similarly flat-topped while the cap rock lasts.
(c) "Knob" areas lying below the Lexington peneplain level, including some greatly dissected areas, near the major streams and some relatively flat. South of Louisville typical knobs, erosion remnants of the Lexington plain, rise above the Scottsburg lowland.
The width of the belt of Knobs varies. In the Louisville region with gentle dip and no faulting it covers a broad zone. In the southern Blue Grass with a bordering fault and steep dip on the southern or downthrow side, the Knobs zone is very narrow. Within the Blue Grass proper a number of isolated knobs are found in areas where the Ohio and Waverly formations have been locally preserved in downfaulted blocks. Such is Burdett Knob in Garrard County, Joe Lick Knob, Madison County, and a number of other such outliers of Ohio shale, and in places Waverly.
Although the region is typically one of rough topography, major stream bottoms are broad and flat. Side-cutting has been rapid in the weak shales and soft sandstones. The Licking River near Salt Lick is a notable example. Down-cutting has been retarded by the Mid-Devonian and lower limestones, and an extensive floodplain has been developed upstream in the shales.
Resources.—Agricultural resources are limited by inferior soil and steep slopes, and the contrast with the bordering Blue Grass region is great. The tops of knobs have been successfully used for orchards. Mineral resources are also limited. Oil shale is a potential resource. The Irvine and associated oil and gas pools of Lee and Estill counties lie in this marginal zone of the Knobs and the Cumberland Plateau. Sandstone for building purposes is quarried in Rowan County. Mineral waters have been important, but are less so now. Clay and shale are widespread but not widely used. Residual clays along the Ohio River and other streams are of the same types found in these floodplains in other regions.