The New River has performed natural surgery for us by cutting the Gorge from Hinton to Gauley Bridge (Figures 1a & b). This cut has exposed a view of the rocks that allows us to understand the present geologic conditions and interpret their geologic history (Figure 2). Such a scene is rare in the world, and consequently geologists take full advantage of these unique canyons. However, it is similar to putting together a jigsaw puzzle with many pieces missing and without the picture on the box.
The stretch going downstream from Hinton to Gauley Bridge is approximately 66 miles long. The river drops 750 feet, or 11 feet per mile. This drop can be visualized by looking down at the river from Hawks Nest, because Hawks Nest is about 750 feet above the river at the same elevation as Bluestone Dam (Figure 3). Just as the river flows toward the north, the average elevation of the surrounding ridges also decreases northward, and the rock layers show this same inclination, or dip. So as one travels downstream, each successive rock layer disappears below the river and out of view (Figure 4).
By examining the rocks along the Gorge, the sequence of layers can be pieced together to produce a cross-section of the entire 66 miles (Figure 4). From this study of rock strata, stratigraphy, the rocks can be placed in chronologic order and grouped together into formations (Table 1). The age of the rocks is determined by the various types of fossils found in them. Similar rock types with similar fossils are grouped together as formations in correct chronological position.
Table 1. Generalized stratigraphic table for the New River Gorge, West Virginia. The seven rock formations (Kanawha, New River, etc.) seen in the Gorge are shown in chronological order, the oldest at the bottom. An eighth unit, unconsolidated alluvium, only occurs along the river bed and banks.
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Alluvium consists of unconsolidated boulders, gravel, sand and silt that make up the floodplain. | |||
| PALEOZOIC ERA | PENNSYLVANIAN PERIOD | POTTSVILLE GROUP | KANAWHA FORMATION
Kanawha Formation consists of 900 feet of shale and siltstone with lesser amounts of sandstone. Contains Gilbert and Eagle coal seams. |
| NEW RIVER FORMATION
New River Formation consists of coal-bearing sandstones, siltstones, and shale. Contains Fire Creek, Beckley, and Sewell coal seams and Nuttall sandstone at top. Maximum thickness is 900 feet in Gorge. | |||
| POCAHONTAS FORMATION
Pocahontas Formation consists of coal-bearing sandstone with lesser amounts of siltstone and shale. Maximum thickness of 400 feet. Contains famous Pocahontas coal seams. | |||
| MISSISSIPPIAN PERIOD | MAUCH CHUNK GROUP | BLUESTONE FORMATION
Bluestone Formation consists of shale and siltstone with lesser sandstone and limestone. Includes Pride shale and Glady Fork sandstone. Maximum thickness is 650 feet. | |
| PRINCETON FORMATION
Princeton Formation is a distinctive 60-foot thick coarse conglomerate that grades into a sandstone. | |||
| HINTON FORMATION
Hinton Formation consists of marine and freshwater shales and siltstones with lesser amounts of sandstone and limestone. Includes Stony Gap sandstone and Avis limestone. Maximum thickness is 1,100 feet in Gorge. | |||
| BLUEFIELD FORMATION
Bluefield Formation consists mostly of marine calcareous shales with minor limestone, siltstone, and sandstone. Maximum thickness is 25 feet in Gorge. |
The rock sequences in the Gorge contain seven formations which can be lumped together into two major groups; the four oldest being of Mississippian age (the Mauch Chunk Group) and the three youngest of Pennsylvanian age (the Pottsville Group). This younger Pennsylvanian Group is distinctive because it is the oldest one containing commercial coal beds in West Virginia. The major boundary between the older Mississippian and younger Pennsylvanian occurs in rocks approximately 325 million years old.
The rocks were originally deposited horizontally as sediments in water bodies and swamps, but today they dip to the northwest at about 60 feet per mile due to subsequent tilting by mountain-building forces that affected all the Appalachians (Figure 5). The geologist can measure the true thickness of each layer, and by adding them together can obtain a total thickness of about 4,000 feet. This is not to be confused with the maximum depth of the Gorge, which is about 1,600 feet. The rock sequence is much thicker because the layers are tilted.
From many studies worldwide, geologists estimate that it took about 7 to 10 million years to deposit these 4,000 feet of sand, mud, and coal. In other words, each foot of rock took approximately 2,000 years to accumulate! The formations of the Gorge thus span a time in Earth's history from about 320 to 330 million years ago. Older rocks are out of view below the river, while younger rocks have been eroded off the mountain tops.
The rocks and fossils that are found in the New River Gorge are the keys to unraveling much of the past. Geologists must also examine the rocks throughout southern West Virginia to get a broader picture of the trends and changes that they have undergone. The geological information that we have today represents over 150 years of work and study by geologists, miners, and oil and gas operators.
The dominant rocks that make up the Gorge are non-marine shales and sandstones (Figures 6 and 7). There are a few exceptions, such as the Avis limestone and Sewell coal (Figures 8 and 9). The shales and sandstones are clastic rocks (they are derived from the erosion and deposition of preexisting rocks). Some are coarse-grained, such as the Princeton sandstone, while others, like the shales, are very fine grained. The coals, on the other hand, are formed from dead plants and trees, some of which can still be identified in the coal.
The characteristics of the rocks and fossils indicate the environment of deposition and to some degree where these clastics came from. It appears that a highland to the southeast, approximately located where the Blue Ridge Mountains are today, was the major source area. Toward the northwest was a shallow, inland sea that was the basin of deposition for the sediments in West Virginia. Further toward the northwest, perhaps in Illinois, was more land of relatively low relief that also supplied some material to this shallow basin. A very close analogy exists today between Australia and New Guinea.
When the rocks are traced from the Gorge toward northwestern West Virginia, the older Mauch Chunk Group gets thinner and thinner. These Mississippian rocks were progressively worn away prior to the deposition of the younger Pottsville Group. This erosion surface between the Mauch Chunk and Pottsville is called an unconformity. Although the unconformity is not obvious or may not be present in the New River Gorge, toward the northwest the entire Mauch Chunk has been eroded away and the Pottsville Group rests on much older Greenbrier limestone.
Another aspect of West Virginia's geological history revealed in the rocks concerns the location of the north magnetic pole and the equator. Many studies worldwide indicate that West Virginia was located south of the equator 325 million years ago when the rocks in the Gorge were being deposited. At that time, the equator traversed northeast from California through the Great Lakes, and the north magnetic pole was located off what is now the coast of Japan.
Two persistent statements concerning the New River are: 1) it is the only river that flows completely across the Appalachians from east to west, and 2) it is the second oldest river in the world. Both of these statements should be examined very carefully.
The headwaters of the New River are in North Carolina, high in the Appalachian Mountains. If we examine this area (Figure 10) it is clear that eight other rivers also have their headwaters high in the Appalachians and all flow westward, but none of these rivers, including the New, completely crosses the Appalachians. Actually, the New River flows north and only turns west after it becomes the Kanawha River.
The question of the "age" of the New River has been debated by experts for a very long time. This is primarily because we do not have a sound method of "dating" the river. However, we can make a number of assumptions that will yield various numbers.
These five caluclations produce ages of 320, 225, 65, 10, and 3 million years. This points out our inability to date the New River. Furthermore, the five calculations make assumptions that may or may not be valid. To calculate the "age" of the New River requires a method based on facts that can be applied to all the rivers of the world. Then, and only then, can we assign the New River to its proper place, be it the 2nd oldest, 22nd oldest, or 102nd oldest river in the world.
*Survey publication.
(Original article by R. F. Fonner, Mountain State Geology, 1987; web page by Peter Lessing, reviewed 1997 and 1999.)
WV Geological & Economic Survey
