Geologists glimpse a heaven below

New York: Imagine the frustration faced for so many years by Eric W. Jordan and his colleagues. They could take a pretty good guess at what lay hundreds of feet beneath the macadam-sealed surface of New York City's streets. They just had no way of knowing for sure.

But the last 10 years or so have been a boon to Jordan and his fellow geologists; mammoth subterranean excavations for the city's Third Water Tunnel, the Second Avenue Subway and the Long Island Rail Road's East Side Access Project have enabled them to see for themselves the rock formations and faults that they had only been able to imagine, undergirding Manhattan.

As a child, Jordan played with blocks, not rocks, but he had an epiphany when he took an environmental geology course at Western State College of Colorado, now Western State Colorado University, in Gunnison. These days, he is truly in his element.

Jordan, 50, works for Parsons, an engineering firm. He has spent countless hours underground, consulting for the Metropolitan Transportation Authority and the city's Department of Environmental Protection on all three multibillion-dollar tunnels, which individually are bringing forth an alternative source of water from the Catskills, the first phase of a new subway on the Upper East Side and a Park Avenue tunnel linking the Long Island Rail Road from Queens to Grand Central Terminal.

The tunneling deep under Manhattan has been fraught with challenges, from disruptive blasting to vehicular congestion at street level and the stifling of retail sales. But it has been a blessing for geologists.

"This is a true moment of discovery, although somewhat inadvertent," said Tony Hiss, the author of "The Experience of Place," a 1990 ode to America's physical reality. "New York's deepest and darkest secret, its oldest and most violent and previously only vaguely glimpsed history is finally coming to light - the schist that formed three-quarters of a billion years ago, when colliding continents compressed an ancient ocean; the even more elusive amphibolite, three times harder than concrete, that's a slow-cooked remnant of islands as big as Japan off the New York shoreline.

"A lot of the theory about what happened down there long, long ago was known, but it had never been seen firsthand by geologists until the multiple sub-Manhattan excavations over the last decade," Hiss said.

The application of that theory illustrates why skyscrapers historically sprouted downtown and in Midtown, but not in between. The bedrock - the formidable Manhattan Schist on which their concrete foundations rest - is closest to the surface in those two areas, though, nowadays, the technology exists to build almost anywhere.

"It's only a matter of what type of foundation you can afford, or are willing to entertain," said Michael Horodniceanu, the president of the transportation authority's capital construction arm.

The dank, vast underground caverns carved by monstrous tunnel-boring machines reveal evidence of the land bridge that existed hundreds of millions of years ago, when New York adjoined what is now Morocco, before the continents ruptured, and of the faults and fractures wrought by vast physical upheavals.

"It gives us a small window to refine our maps and get a better understanding of regional geology and of the bedrock that formed in Pangea when the continents collided," Jordan said. "It gives us a chance to document the behavior of Manhattan's bedrock while advancing

tunnels, and to provide a history of tectonic events. Lastly, mapping provides a geological record for posterity and use by future generations."

In the tunnels, the bare walls are layered with volcanic rock, folded taffylike, the result of enormous pressures and high temperatures. The bedrock later cracked during earthquakes. Jordan likened it to removing a Charleston Chew candy bar from the freezer and slapping it on the counter, shattering it.

No fossils have been discovered, he said, because had they existed the immense heat and pressure at depths of as much as 5 miles would have burned the organic matter beyond recognition.

"The geology of Manhattan is as interesting as its people, art, history and politics," Jordan said. "The processes of our Earth's interior placed incredible force, producing extreme temperature and pressure creating both ductile and brittle deformation of the underlying bedrock, and provides evidence substantiating Alfred Wegener's once-ridiculed theory of continental drift." (The theory by Wegener, a German geophysicist, was not widely accepted until the mid-20th century, well after his death in 1930).

"Geologists played an important part, reducing risk during the excavation phases of the new tunnels, and in turn got a glimpse of the buried, incredibly complex and dynamic, physical underpinnings of our city," he said.

The Manhattan Schist Formation is the best known of the local metamorphic rock formations, and is visible in the outcroppings in Central Park. The region is also defined by the Hartland Formation, and by Inwood Marble and Fordham Gneiss, which is older and predominates on Roosevelt Island, along the Lower East Side and in the Bronx (where it is prominently emblazoned with the Columbia University "C" at Spuyten Duyvil). There is schist festooned with garnets, forest-green amphibolite, salmon-hued pegmatite and crystalline feldspar, quartz and mica.

Beginning with topographical maps drawn as early as 1865 by Egbert L. Viele, which showed his survey of the original streams, marshes and coastline of New York City, geologists have identified stream channels in the tunnels, where there may be weak zones that require reinforcement below.

"Pre-excavation geological assumptions were, by and large, accurate," Jordan said. He describes New York's geology as unique: "Very strong and very good quality, which can support tremendous loads and stand on its own temporarily, in most places, until it gets support, to replace excavated rock." (Excavated rock from the current subway and railroad projects has wound up as landfill for Brooklyn Bridge Park and the Ferry Point Park golf course in the Bronx.)

Hiss, the author, hopes the transportation authority will capitalize on the man-made caverns when the East Side Access tunnel is completed, in order to show off the city's third dimension at Grand Central Terminal: "Not skyscrapers this time, but depth-scrapers, the solid basement that makes the skyscrapers possible," he said.