http://www.nytimes.com/2014/07/03/ny...city.html?_r=0
Excavation for Railyard Project Reveals a Hidden Piece of New York City
JULY 2, 2014
By DAVID W. DUNLAP
Quote:
If you think the crush is bad around Pennsylvania Station these days, you should have been here 465 million years ago.
“This rock has been subjected to three periods of continental collision,” the geologist Sidney Horenstein said, as he stood in a railyard west of the station, examining a wall of gray Manhattan schist with swirls of white pegmatite.
It looked like a giant marble cake. One that has broken many drill bits.
“The rock was squeezed and squeezed again and squeezed again,” he said, referring to what happened in the Taconic, Acadian and Alleghenian orogenies. These mountain-building events, hundreds of millions of years ago, shaped North America and left fascinating traces in New York City.
Some of those traces have come to light in the railyard over which Brookfield Office Properties is developing a mixed-use project, Manhattan West, beginning with a platform that will cover the entire yard.
New Jersey Transit and westbound Amtrak passengers know this yard well. It offers a glimpse of the city before trains funnel into the North River Tubes. By the end of the year, passengers will no longer see daylight until they reach North Bergen, N.J.
Brookfield’s project also involves the excavation of bedrock on either side of the tracks, down to about 30 feet, exposing geological features that have never been seen. So when I was invited to watch the assembly of the platform, I asked Mr. Horenstein to come along.
Mr. Horenstein, 77, the environmental educator emeritus of the American Museum of Natural History, is a lively guide. With affection and humor (“The Bronx is gneiss”), he can make rocks come to life.
“Not a fossilized snake but a folded intrusion,” Mr. Horenstein said of a twisting deposit under 31st Street that appeared to have been traced from splayed fingers. He marveled at this evidence of compression and deformation from the collision, or collisions, of the vast plates composing the earth’s crust.
Through Mr. Horenstein’s eyes, Manhattan schist, the bedrock from which the towers of New York rise so confidently, looked as malleable as liquid.
And with good reason. “These were deposits of mud on the sea floor,” Mr. Horenstein said. “Heat and pressure squeezed these layers and recrystallized them into schist” — after intermediate periods as shale, slate and phyllite.
The resulting folds are easy to see, because molten pegmatite penetrated the voids. Pegmatite has a high quartz content and thus provides terrific contrast to the dark schist.
Brookfield executives do not look upon pegmatite so kindly.
“It is particularly hard on drills and equipment,” said Henry Caso, the vice president in charge of constructing Manhattan West.
From a builder’s point of view, schist and pegmatite are a blessing as well as a curse. The presence of so much rock permits Brookfield to proceed with its unusual plan for Manhattan West, a $5 billion project that is to be finished in 2019.
Office towers are to be built at Ninth Avenue and 31st Street and at Ninth Avenue and 33rd Street. An apartment building is to be constructed at Dyer Avenue and 31st Street, opposite a hotel at Dyer Avenue and 33rd Street. An existing building over the west end of the yard, 450 West 33rd Street, is to be reclad in glass so that it conforms with the rest of the complex.
The new buildings will sit not on the platform, but on the bedrock outcroppings along the north and south edges of the railyard. However, parts of the office towers will cantilever over the platform, which is to become a tree-lined plaza.
The platform is composed of enormous, hollow concrete segments. They are 6 feet wide, 15 to 30 feet long and more than 12 feet high. They weigh up to 56 tons each. Thirty-nine of these segments are needed to stretch across the whole railyard.
A traveling crane picks up the sections and assembles them on a temporary platform above the tracks. The sections are epoxied together and lashed with steel cables. Pulled taut, these cables create so much tension that the sections become a self-supporting structure, after which the platform can be removed.
By analogy, imagine holding a half-dozen building blocks together with a tight rubber band. You could turn that stack horizontally and it would hold.
“Amtrak has reviewed and approved the design of Manhattan West,” said Craig Schulz, a spokesman for the railroad, “and continues to work cooperatively with the developer throughout construction to ensure the safety and security of our passengers is not compromised.”
As we made our way through the yard, however, it seemed that all the talk of upheavals in the earth’s crust was beginning to get to Mr. Caso.
“You don’t think we’re due for another collision, do you?” he asked Mr. Horenstein.
“Not yet,” the geologist said reassuringly. “Not for another 50 million years.”
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