Dr. Roland Harper, a pioneer Alabama botanist/geographer, wrote in 1906 that “Tuscaloosa is probably at present the most convenient point in the eastern United States at which to study the boundary between the Paleozoic region and the coastal plain...” This is still true today and Hurricane Creek is the most accessible place in Tuscaloosa County to see that “boundary” – the place where the Appalachian (Paleozoic rock area) ecosystems meet and interact with the coastal plain ecosystem.
In North America, the Paleozoic era began with deep sedimentary basins along the eastern, southeastern, and western sides of the continent, while the interior was dry land. As the era proceeded, the marginal seas periodically washed over the stable interior, leaving sedimentary deposits to mark their incursions. During the early part of the era, the area of exposed Precambrian, or shield, rocks in central Canada were eroding, supplying sediment to the basins from the interior. Beginning in the Ordovician Period, mountain building intermittently proceeded in the eastern part of the Appalachian region throughout the rest of the era, bringing in new sediments. Sediments washing from the Acadian Mountains filled the western part of the Appalachian basins to form the famous coal swamps of the Carboniferous Period. In North America carboniferous is not generally used instead the time is divided between Mississippian and Pennsylvanian period because of differences in the sedimentary rock deposited in this time. The Mississippian is characterized by limey sediments deposited in shallow seas, typically with abundant crinoidal fossils. The Pennsylvanian typically is characterized by terrestrial sediments such as sands, shale and most importantly coal. Most of our oil and gas are obtained from Pennsylvanian sediments. Tuscaloosa County in particular is rich in Pennsylvanian-era deposits, and this site exemplifies the Pottsville Formation. Relative age dating of the Pottsville places it in the early to mid Pennsylvanian period, or roughly 300 million years ago. During this geological period, much of what is now the central United States was covered by a shallow sea, the Rocky Mountains did not yet exist, and the Appalachians were much higher than today.
Going from downtown Tuscaloosa to Hurricane Creek by road takes you across the Fall Line Hills portion of the Gulf Coastal Plain. Sand, gravel, clay and ironstone underlie the area. Turning north on Hwy 216 and going downhill to Hurricane Creek takes you into the Appalachian terrain – the Pottsville Formation appears with its sandstone, shale, conglomerate and of course, coal. Throughout history, coal has been used as an energy resource, primarily burned for the production of electricity and/or heat, and is also used for industrial purposes, such as refining metals. A fossil fuel, coal forms when dead plant matter is converted into peat, which in turn is converted into lignite, then sub-bituminous coal, after that bituminous coal, and lastly anthracite. This involves biological and geological processes that take place over a long period.
Coal (from the Old English term col, which has meant "mineral of fossilized carbon" since the 13th century) is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Dr. Michael Tuomey, Alabama’s first state geologist published a report in 1847 on Tuscaloosa County’s coal and iron resources. He reported finding six coal seams on a branch of Hurricane Creek and still more further downstream. This report led to literally hundreds of mines being dug into the bluffs along Hurricane Creek. The mines were low “belly mines” where miners literally lay down on the job in mines less than three feet high. Coal was often dragged out in tow sacks. Most of these mines (over 125 are known in the “M Bend” area) were abandoned by the 1930s, but in those hard times of the depression, many people crawled into the old mines to dig the coal from the support pillars left by the miners. This was a very dangerous way to get free fuel, and it left large unsupported ceilings. Thus, after the nearby Summerfield subdivision was built in the 1970s, most of the mines entrances on the main creek were sealed by a mine safety agency.
As noted earlier, Hurricane Creek is a boundary area; here Appalachian and Gulf Coastal Plain plants meet. Here strange combinations occur. On the coastal plain, the main evergreen shrub along the stream banks is Florida anise (Illicium floridanum), while mountain laurel (Kalmia latifolia) occupies the same niche in the Appalachian areas. At the “M Bend” site both are present. Dr. Eugene Allen Smith, Alabama’s second state geologist, found a rather rare small tree at the “M Bend” before 1900. This beautiful little tree – the silky camellia (Stewartia malacodendron) was not reported again for over 100 years, until George Wood spotted it in 2002.
The Hurricane Creek area features tall sandstone cliffs with beautiful “box work” formations and a creek with sandstone boulders. To see Hurricane Creek today is to see, albeit on a smaller scale, what the Black Warrior River looked like before it was dammed. Hurricane Creek is the last free-flowing Appalachian-type stream which can be seen before the Black Warrior River reaches the Fall Line at Tuscaloosa.
A fall line (or fall zone) is the geomorphologic break between an upland region of relatively hard crystalline basement rock and a coastal plain of softer sedimentary rock. A fall line is typically prominent when crossed by a river, for there will often be rapids or waterfalls. Many times a fall line will recede upstream as the river cuts out the uphill dense material, often forming “c”-shaped waterfalls. Because of these features riverboats typically cannot travel any farther inland without portaging, unless locks are built there. On the other hand, the rapid change in elevation of the water, and the resulting energy release, makes the fall line a good location for water mills, grist mills, and sawmills. Because of the need for a river port leading to the ocean, and a ready supply of water power, settlements often develop where rivers cross a fall line, including, of course, Tuscaloosa and Northport.
To log this earthcache, you must answer the following questions. Send them to me via my email address on my profile. Do not post them to your log or it will be deleted.
1. During what geologic period was the Pottsville Formation created? How long ago did it occur?
2. Do you see any evidence of the numerous coal mines that once dotted the landscape here? Why or why not?
3. At GZ there is a large slab of exposed sandstone. What is the length of this rock slab at its widest exposed point?
4. What part did water play, if any, in the formation of this slab of rock? Can you observe any indication of that on the spot where you stand?
5. (Optional) Take a photo of yourself (or your GPS) in front of the rock formation to verify that you visited this site.
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