Posts in Geology

Road cuts: Windows to the Past

Written By | April 19, 2014 | Posted in Geology | No Comments

Physics, astronomy, chemistry, biology, anthropology… There are many, many fields of exploration, each with its own terminology, tools of the trade, and area of expertise. Each provides its own unique window into the past and offers its own angle on why the world is the way it is today. The one which tells us the most about the ground beneath our feet is geology. There are many tools to the geologists’ trade, but few are as easily accessible as road cuts.

When a highway is cut across the countryside, engineers must deal with many obstacles. Among them, rivers and marshes need bridges, loose soil needs bolstering, and hills need breaking. The last of these produces a geological gold mine. You don’t have to drive far down a highway to see places where engineers blasted through the rock to make a straighter, smoother path for the road. All across America, highways are lined with miniature grand canyons, though formed through the power of TNT rather than the Colorado River (actually, road cuts typically use an ANFO-based explosive).

Road cuts range from just a few feet to hundreds of feet. One particularly impressive site is Sideling Hill in western Maryland (picture at the top of the post) where 810 years of Mississippian formations are exposed. In this case, Mississippian does not refer to geography or anthropology but to a geological period spanning 323-358 million years ago.

Impression fossil

It is not unusual for various fossils to be found close to the surface of road cuts. Prior to his recent debate with Ken Ham, Bill Nye the Science Guy pulled over at a road cut along the way where he “easily picked up three nice specimens of rock revealing several fossilized small shelly ancient sea creatures” (Skeptical Inquirer). In many of these road cuts, such as the one at Sideling Hill, the fossils are present but may not be obvious. Sideling Hill contains many fossils of plants and marine animals which more often than not are present as impressions rather than the more intact fossils that typically come to mind.

Road cut

Road cuts are exciting because of how accessible they are to everyone. A short drive can take you to a place where you see millions of years into the past and have a very real chance of finding ancient fossils. During the Mississippian period, North America was under water, covered by a vast but relatively shallow sea. The Appalachian Mountains were just beginning to form and the reign of the trilobites was slowly winding down, though they had a few tens of millions of years left before eventual extinction.

When you stand before a road cut, imagine trilobites swimming in an ancient sea, not knowing their days are numbered. Imagine the plentiful Ostracoda, a critter nicknamed the seed shrimp. Right at that spot, hundreds of millions of years ago, the great-granddaddy of the dragonfly, the Meganeura, may have flown by, finding refuge in the Appalachian orogeny. Let road cuts be a window into the past and a doorway where science meets imagination.

Every step you take is literally on the shoulders of our ancient ancestors. Stop by a road cut and take a moment to say hello.

Recommended reading:

Annals of the Former World Annals of the Former World by John McPhee.

A little dated but still quite interesting and informative, this Pulitzer-prize winning book is actually a collection of five of McPhee’s books on geology which gives a glimpse into the geology of America, the geologists doing the science, and even some intriguing glimpses into early American life in the regions under consideration.

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