TheHighland Rim is a geographic term for the area inTennessee,North Alabama, andKentucky which surrounds theCentral Basin.[1] The Central Basin is a geologicaldome which has subsequently fractured and eroded to produce a basin.[2] The Highland Rim is acuesta surrounding the basin, and the border where the difference in elevation is sharply pronounced is anescarpment. Their feature continues well intoSouthern Indiana and intoCentral Indiana as theIndiana Uplands.[3]
The Highland Rim is aphysiographic section of the largerInterior Low Plateaus province, which in turn is part of the largerInterior Plains physiographic division.[4] Most of the Highland Rim is located in U.S.EPAEcoregion 71, Interior Plateau, which is a part of theEastern Temperate Forest.
The sections of the Highland Rim are referred to the four cardinal directions, e.g., "Northern Highland Rim", etc. The Highland Rim is rather continuous and any division of it, including the ones made below, are somewhat arbitrary. The term "highland" here is relative: it is certainly higher than the basin it surrounds, but it nonetheless is seldom at an elevation above 1,100 feet (340 m) above sea level and never more than about 1,400 feet (430 m) above sea level except where interrupted, primarily to the southeast, by outliers of theCumberland Plateau. With the exception of a few broad stream bottoms, the land is characterized by ridges and valleys with a few fairly low hills. The entire region is well watered with many perennial streams. There are occasional waterfalls which sometimes delineate the Highland Rim from the Central Basin which it surrounds.
The Western Highland Rim is encountered a few miles west of Nashville and extends to the western valley of theTennessee River.[5] The area is hilly, ranging from about 400 to 1000 feet in elevation,[6] and is bisected by theTennessee River and theCumberland River valleys.[7] Underlying bedrock of the region is chieflyMississippianlimestone,chert,shale, andsandstone with exposures ofDevonian,Silurian,Ordovician, andCambrian limestone, chert, and shale.[8] In the northern part of the Western Highland Rim,sinkholes readily occur in an area with a southern extension of the Pennyroyal plateau of Kentucky, where thekarst is best developed on theMississippianSt. Louis Limestone and theSte. Genevieve Limestone.[9] Some farming is done in the flatterinterfluves, and in stream and river valleys.[6]
The Eastern Rim rises approximately fifty miles east of Nashville and is bordered to its east by even higher terrain, theCumberland Plateau. Erosion has exposed carbonate bedrock of LatePaleozoic age. These carbonate rocks contain variable amounts of chert and are often interbedded with fine grained clastic rocks. As a result, these rocks are more resistant to erosion than the underlying purer limestones of the Lower (Early) Paleozoic. The geology is diverse and istypically limestone at valley floors (around 500 feet (150 m) elevation) and sandstone on ridges (to around 1,000 feet).[10] The constituent bedrock is composed primarily ofMississippian agedSt. Louis, andWarsawlimestones withFort Payne chert underlain byChattanooga Shale that forms a large part of the escarpment.[8] This area is flatter than the Western Rim, characterizable astablelands of moderate relief combined with irregularplains.[6]
The Northern Highland Rim is encountered a few miles north of Nashville and extends to theKentucky border, and the region of Kentucky adjacent to it called thePennyroyal is largely a continuation of it under another name as is theIndiana Uplands, located to the north of theOhio River.
For the most part the Southern Rim is the farthest from Nashville, rising at some points just a few miles north of the border withAlabama. The landforms are continuous with those in adjacent portions of Alabama, although perhaps the most spectacular landforms of any portion of the Rim are to be found there.
The stratigraphy of the Southern Highland Rim is primarily composed of flat-lying limestones,dolomites, and shales, and to a much lesser extent, of cherts,siltstones,mudstones, and very fine grained toconglomeratic sandstones.
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