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August 21, 2016 Weekly Geology Guess

August 21, 2016
Greetings from the Bluff Park   Porch, way up yonder on Shades Mountain (1,109′) in Alabama:

My discussion on Alabama Geology will continue with the Geologic Time Scale or the Geologic Column and the critters that abide within each pigeon holes.

As with most sciences, especially natural sciences, we love to pigeon hole our data.  Most of the pigeon holes have scientific merit and accuracy.  With the Geologic Time Scale we start with the oldest layers and work upward to the youngest layers.

For some of you this will be new, novel, and maybe heretical.

Expedition Earth: Geological time scale

Silurian Period

We will now enter the land of the the Celtic tribe of the Silures.

Note:  As a geologist we usually do not talk in number of years but in periods, epochs, and eras.

“The Devil is in the Detail”

Not only with each period do we have unique animal and critter assemblages, geography, but also some type of plate tectonics or mountain building is going on.

“The Silurian is a geologic period and system that extends from the end of the Ordovician Period, at 443.8 million years ago (Mya), to the beginning of the Devonian Period, 419.2 Mya.”

Plants & Animals:    “A significant evolutionary milestone during the Silurian was the diversification of jawed and bony fish. Life also began to appear on land in the form of small, moss-like, vascular plants that grew beside lakes, streams, and coastlines, and also in the form of small terrestrial arthropods. However, terrestrial life would not greatly diversify and affect the landscape until the Devonian.”

Geography:    “With the supercontinent Gondwana covering the equator and much of the southern hemisphere, a large ocean occupied most of the northern half of the globe.[14] The high sea levels of the Silurian and the relatively flat land (with few significant mountain belts) resulted in a number of island chains, and thus a rich diversity of environmental settings.”

Tectonic Events:    “When the proto-Europe collided with North America, the collision folded coastal sediments that had been accumulating since the Cambrian off the east coast of North America and the west coast of Europe. This event is the Caledonian orogeny, a spate of mountain building that stretched from New York State through conjoined Europe and Greenland to Norway. At the end of the Silurian, sea levels dropped again, leaving telltale basins of evaporites in a basin extending from Michigan to West Virginia, and the new mountain ranges were rapidly eroded. The Teays River, flowing into the shallow mid-continental sea, eroded Ordovician strata, leaving traces in the Silurian strata of northern Ohio and Indiana.”

Alabama Paleontology and Geology:    “Most of Alabama lay beneath the sea throughout much of the Silurian, as evidenced by fossils of brachiopods, trilobites, crinoids, and other marine creatures. Erosion of the Taconic Mountains to the east deposited sediments in these shallow seas. One particular type of sediment produced layers of hematite iron ore, which has played an important role in Alabama’s industrial history. Although not shown on this map, these hematite layers are exposed in the Valley and Ridge Province near Birmingham and Gadsden in central Alabama. Their easy accessibility led to the state’s once thriving iron and steel industries.”  The Paleontology Portal

Alabama Silurian Rocks or Units include the Red Mountain Formation (The Silurian beds are shown in red on the attached Alabama maps)  Some of the Silurian? – Devonian Low-Grade Metamorphic Rocks include the Jemison Chert, Butting Ram Sandstone, Cheaha Quartzite, to name a few.

Silurian Life includes trilobites, graptolites, conodonts, corals, stromatoporoids, mollusks, first fresh water fish, first jawed fishes, spiders and centipedes on land, and the earliest fossils of vascular plants.

As with most of my weekly fores into geology, with each topic I could write many papers and dissertations.

Note:  I have intentionally reduced the amount of linked graphics in this email due to the amount of space required and trying to untangle everything the following week has been a mess.


References include:


–    Wikipedia


Editors Note:  It is the intent of this site to keep this discussion as simple as possible, so as to educate the interested general public and not to discuss with the geology crowd the latest geologic theories and nuances.  Thanks, R


“No copyright infringement intended.
The rights belong to their respective owners”
Copyright Disclaimer: Under Section 107 of the Copyright Act 1976, allowance is made for “fair use” for purposes such as criticism, comment, news reporting, teaching, scholarship, and research. Fair use is a use permitted by copyright statute that might otherwise be infringing. Non-profit, educational or personal use tips the balance in favor of fair use.


Author’s Request:  If you see any pictures that you know the source and photographer, let me know immediately.  Thanks!  R

Images have been searched by TinEye Reverse Image Search.


Next time we will venture into the Devonian Period.


Enjoy the adventure!



Silurian World Map.

Silurian World Map.

AL Geo. Map, Cumberland Plat.

AL Geo. Map, Cumberland Plateau

AL Geo. Map, Highland Rim

AL Geo. Map, Highland Rim

AL Valley and Ridge Geology

AL Valley and Ridge Geology

Silurian Sea Life

Silurian Sea Life


Silurian Fish, entelognathus, Ynnan, China. by gogosardina d6nx55p

Silurian Graptolite, Spirograptus.

Silurian Graptolite, Spirograptus.

Silirian, Trilobite, New York trimerus delphinocephalus

Silirian, Trilobite, New York trimerus delphinocephalus

Silurian Terrestrial Plant, Cooksonia sp.

Silurian Terrestrial Plant, Cooksonia sp.

Red Mt. Fossils

Silurian, Red Mt. Fossils – brachiopods, Birmingham, AL.

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