The geology of some of the land I dig on with the dogs.
One of writer John McPhee's best little gems is a long essay called "The Gravel Page" which was first published in The New Yorker, and later reprinted in the McPhee essay collection entitled Irons in the Fire.
"The Gravel Page" is about forensic geology, which sounds like an absurd topic until you realize there are people so studied in the shifting sands, alluvial deposits and quartz formations of the world, that they can look at the dirt under your car's fender and tell you where in the world it came from.
And they can get it right within a mile or two. Amazing.
The Gravel Page is more than excellent writing -- it is also good story (always that!) mixed with an exploding cosmos of knowledge and a new way of looking at the world. This is non-fiction writing at its best.
I bring up John McPhee because I recently got two different emails about soil structure. One was about New Jersey soil as sandy and easy to move as cake mix, the other about Vermont ground so riddled with rock it requires three people, a pickax, and a steel digging bar to consider working a terrier to ground.
In truth, we are a large and varied country and though we are one land, we are many soils. In fact, as odd as it sounds, about 20 state legislatures have actually named their state soils.
Indiana's state soil is called "Miami" (no doubt named after the Indian tribe), while New Jersey's is called "Downer," and is described as "a grayish sandy loam."
Vermont's state soil is thin stuff called "Tunbridge" which is described as being "20 to 40 inches deep over schist, gneiss, phyllite, or granite bedrock."
Virginia's state soil is something called "Pamunkey." No one I know of has ever heard of Pamunkey, but it is described as the type of wash-down found along the banks of the James River and "which originated in every physiographic province in the Commonwealth and therefore represents the WHOLE state better than other soils."
Ah, a political soil invented by a committee and named after a tribe. Of course.
Maryland's state soil is something called "Sassafras" which is described as "a Benchmark and Hall of Fame soil series." Really? There's a Hall of Fame for soil?
In truth, the Maryland dirt in which I dig defies all categorization. You may have good friable soil in a field, but 50 yards away will be a belt of trees and an area packed with cobbles and hard marl. A small ridge above the field may be of igneous rock so hard it could be used as an Easter Island hammer stone. Everywhere -- seemingly without rhyme or reason -- you will find broken pieces of shale mixed together like playing cards dropped by God Himself. What kind of soil have you got? We've got it all!
I know about the soil in my neck of the woods from digging on it. This is not book knowledge. That said, I was rather pleased last night when I came across a web site with maps of Maryland soil by County, and with enough detail that I could identify the location of individual farms where I have been digging on the dogs. I cannot read much out of the maps yet, but I will drill a bit and see if I can sort it out. These maps, after all, are the back story of this land.
The geology of this region is not a simple one. I live and dig near the area where Maryland, Virginia and West Virginia come together. A fall line shoots through the middle of it, and the ocean is not far away.
To the West lie the Appalachian Mountains, one of the oldest mountain ranges in the world, worn down to a few thousand feet from peaks that may have once been as high as the Sierra Nevadas.
To the East is the sandier soil of the coastal flats and the Delmarva Peninsula.
The Piedmont -- the geology of the area I think of as my home -- is the area that lies in between. These are the ancient foothills of the Appalachian mountains. Here most of the old rock has degraded to good soil, but there are still regular ridges of very hard stuff that Mother Nature and Father Time, working together, could not reduce to rubble.
The area I call the Piedmont Breaks is the area running roughly parallel to Route 95 and is normally called the "Fall Line". This is the very edge of the Piedmont -- a kind of geological no-man's zone between the true Piedmont and the Coastal Plain.
Here the continental plates of Europe and Africa have ground up against North America. As the continents crashed into each other, ancient rock folded up and ancient sea beds were pushed far inland. The last really major geological event in this area was the break up of Pangaea during the Mesozoic era as Africa pulled away from North America, forming large basins and shallow seas (the so-called Iapetus Ocean) that teamed with wildlife. The bits and pieces of broken shale I find all across this area are the vestigial remains of those vast mud-filled basins and ocean shelves.
My own house, quarried from local gneiss and roofed by Vermont Slate, sits almost on top of the Fall Line that is the boundary line between the Piedmont and the Coastal plain.
The house itself sits on a rocky knoll about an eighth of a mile back from the Potomac River. There has been no significant geological activity in this area for many thousands of years, and ground pressure is receding not building. I am not worried about my property values being decimated by an earthquake. About terrorism I am a little less certain -- the Pentagon is only a mile and a half away.
The path down to the river is a gentle slope most of way, but that path ends at a sheer 90-foot rock cliff that goes down to the river. The only way to descend this cliff is to pick your way down steps hewn into the cliff next to a small waterfall. It can be treacherous going in winter.
If you turn left at the base of the cliff, you can walk up the river bank to Chain Bridge about a quarter mile up. If you are traveling in a small boat, you can go no farther that this due to rocks, rapids and falls. Above Chain Bridge is Little Falls, and above that is Great Falls, a stretch of water sufficiently treacherous that it takes the lives of half a dozen people a year -- mostly young fools and foreigners who ignore the warning signs posted in a half dozen languages at water's edge.
I am told this is the steepest and most spectacular fall line rapids of any river in the eastern U.S. The falls were once located at Chain Bridge but over many millenia they have chewed their way upriver to where they are now, in Mathers Gorge.
If you turn right at the bottom of the cliff below my house, you will reach Key Bridge about a quarter of a mile away. This is the bridge that crosses the Potomac River into Georgetown, and it is the way I normally get into the city.
If you were to put a boat into the water just below my house, turn downstream, and paddle 13 miles or so, you would slide pass Mount Vernon -- George Washington's old home. Keep on going and you will reach the Chesapeake Bay. Keep going from there, and you can reach the Caribbean, Paris, London, South Africa, Malaysia, New Zealand, California, and South America. To be on a river with unobstructed passage to the sea is to be connected to quite a lot.
A river at your door is a great thing. Rivers last because they totally renew themselves every 24 hours or so.
The soil lasts because it remains locked up in a vault of its own making.
I am pretty sure that not much else lasts.
We make our headstones out of rock in an attempt to find a kind of store-bought immortality, but after 100 years the names and dates are as meaningful -- and as meaningless -- as hieroglyphs.
Not much else lasts either. I dig on land that has been farmed for over 300 years, and on much of it parts of the Civil War were hard fought.
Yet there are no bones to be found, no bullets, no buttons, no bottles. Dinosaurs and deer have lived and died on this land for eons, and yet they have left not a single mark behind. Trees and bushes have risen (and fallen) for thousands of millennia but they too have left no sign of their existence except (perhaps) the soil itself.
In a thousand years, I have little doubt that almost nothing extent today will be intact and recognizeable. But the river will still run through Mathers Gorge, and the soil maps made in 1950 will still be good.
"By the sweat of your brow you will eat your food
until you return to the ground, since from it you were taken;
for dust you are, and to dust you will return."
. . . - Genesis 3:19
Great Falls on the Potomac
This is a repost from May, 2007