The Antiquity of Blacksburg

Howard Shaeffer Avery, VPI '28

Five hundred million years ago (more of less) limestone was being deposited in the bottom of a shallow sea that occupied the position of the present Appalachian mountains. How do we know this? Because limestone is deposited only on the bottom of oceans, and Blacksburg rests on about six thousand feet of limestone. Are you still doubtful? Then how do you explain the sea shells in the limestone at the base of Bald Knob?

The processes of geology never stop. They are acting just as surely now as they did when the world was young. Look at any swollen stream in the spring-time. It is not carrying a heavy burden of sand and mud to the ocean? Does the stream ever flow backwards? If not, where does all the sand and mud come from? The mountains are the source of the sediments but, given time, will not the mountains wear down? What replaces them when they are worn flat and the land is a plain?

Five hundred million years ago the winds and the rains tore at the massive peaks of the ancestor of the Blue Ridge, just as they tear at the Peaks of Otter today. The freezing of water in cracks of the rocks split off large pieces. The streams tumbled and tossed the splinters and ground them against other fragments until only a handful of sand and pebbles remained. The sand was carried to the sea and became beaches along the shore. In time the sands compacted and became rock, and we have massive sandstone formed.

Out in the depths of the sea beyond the reach of the sands of the shore tiny marine animals were living and dying, and their limy shells, mingling with the finer mud from the rivers, became shaly limestone. Life was microscopic in those days. A few beetle-like trilobites were the lords of the earth, and their few petrified remains are almost our only record of the dynasties of the early days of Blacksburg.

It took a hundred million years or more to make the immense deposits of limestone that are the foundations of Blacksburg today. Life developed, the stronger marine animals thrived while the weak died out, and in the course of time the sea swarmed with mollusks, brachiopods, trilobites, and bryozoa, whose dead bodies sinking in the ooze of the ocean became pages in the books of prehistoric time. The reign of the trilobites was overthrown and the brachiopods became the masters of the earth. A few corals appeared, and some of their remains can be seen near Newport today; the fossil remnant of one of the oldest coral reefs in the world.

The beds of limestone became thicker as the bottom of the ocean slowly sank beneath the enormous pressure of the tons of sediment being deposited. The land became flatter as the material was worn off, until wide rivers were slowly meandering across great plains only a few feet above sea level. The sluggish rivers could carry but little sediment, leaving a thick blanket of soil to accumulate on the surface of the land. The rivers ceased to bring mud to the ocean and pure limestone was deposited on its bottom. Erosion was at a standstill.

Nothing is constant except constant change. If the forces of erosion were still, those within the earth were not. They acted, the land was raised, and the eroding elements began anew. The thick blanket of soil was rapidly washed into the sea, becoming a vast deposit of shale. Ever hungry cephalopods swarmed the oceans, gobbling up the myriads of defenseless graptolites brachiopods. In the shale near Luster's Gate dozens of the rod-like arms of the graptolites can be found, while one large cephalopod can be seen entombed in the stone by the side of the road; a petrified graptolite eater of long ago.

Sandstones followed the shale and more shale was deposited on top of the sandstones. Then came a thick deposit of sandstone, the rock that forms the top of Brush Mountain today. Occasionally fern-like plants thrived in abundance and their remains filling the muck at the bottom of the swamps became beds of coal when crushed under the pressure of the ever-depositing sediments. Thus began Blacksburg's coal industry.

Some of the sea denizens crawled out on the shore and learning to breathe the air became the first land animals. Larger fishes developed, sharks appeared, corals thrived, and the seas were filled with life and the air with the hum of myriad insects. Swamps were everywhere and the greatest coal deposits of the world were laid down at this time. Thousands of feet of sediments were deposited in the ocean and its bottom groaned beneath their accumulated weight.

Miles of sediments were too much for the thin crust of the earth, and about three hundred million years after the limestone of the Shenandoah Valley of Virginia was deposited, the earth rebelled. The Blue Ridge humped its back and lifted, pushing the sediments and rocks aside as if they were mud, lifted and pushed until the rocks were strained and twisted and the minerals of the granites were stretched and squeezed until some of them were as flat as pancakes. High into the air the accumulated sediments were lifted and higher still the Blue Ridge lifted its granite ridges. So high that after two hundred million years of weathering they are still our highest mountains.

But what of the sedimentary rocks? Some were twisted and folded, some cracked, broke, and slid up on each other, and some crumpled like putty under the terrible strain. The rocks of Blacksburg were pushed to the flanks of Bald Knob and limestone from around the site of Christiansburg was pushed miles over the surface, finally to come to rest as the foundations of Blacksburg.

Then the age old processes set in. The winds and rain wore down the rocks, smoothed the surface, and once more Montgomery County was flat. New River meandered over wide plains in great loops and bends, as a river can do only in flat country.

Again the land was raised, but more slowly than before, and New River kept pace with the uplift by wearing down its channel, preserving its loops and bends in a rough and hilly country. The elements still wear at the land but the time since then has been short and they have not worn it flat. The limestone dissolved easily and valleys now marks its location. Underground it was dissolved to form great caves, the grottos of the Shenandoah Valley. The shales eroded less easily and now are found on the slopes of mountains, but the sandstones resisted the elements and now stand up as peaks and ridges.

But what of life? It went serenely on, living eating, fighting, dying, but ever changing. Reptiles appeared in the swamps, swam in the sea, and developing wings, flew in the air. They became larger and fiercer until finally they were the lords of the earth. They had bodies weighing tons but brains weighing ounces. They knew only enough to eat and fight. They were the largest and fiercest animals on earth and they feared nothing.

But where are they now? The weak, defenseless mammals exterminated them. The reptiles laid eggs and, lacking brains, did not protect them. The small, fleet mammals liked nothing better than a meal of dinosaur eggs, and their appetite being insatiable the reptiles died out for want of children.

Grasses appeared, mammoths, dogs, horses, and finally man. The undisputed master of the earth looks back on the long line of extinct animals and wonders if he is to follow their course- die out as they did because he cannot adapt himself to changing environment.

Curious reader; do you wish to see these things for yourself? If so, stand on Lover's Leap and see the way New River meanders along steep cliffs. Follow it through Gap Mountain and explain, if you can, how it cut such a channel. See for yourself that the rocks of Brush and Gap Mountains are sandstones harder than the shales of the slopes or the soft limestones of the valleys. Look out over the tops of the hills and see that they are all on a level, showing the existence of a former plain. Look for the fossils at the foot of Bald Knob and in the shale of Roanoke Valley. And finally, follow the Virginian Railway as it cuts across Gap Mountain and measure the thickness of strata, every foot of which took years to form, and observe the folding from the force of the uplift. Look, think, and then, if you will, doubt.

(From Virginia Tech Engineer, vol. 4, no. 1 (November 1928), pp.13-24)


Return to Other Documents, Old and New


http://spec.lib.vt.edu/bicent/recoll/antiqui.htm
¤
Last updated May 1, 1998