The leafy N + N compounds of fall

leaf slime and leaf sludge — appearing in a NYT story on the autumnal travails of the Metro-North Railroad, “The Dirty Side to Changing Leaves: Leaf Slime on the Region’s Rails” by Jonathan Wolfe (on-line on the 22nd; in print, “On Train Tracks, a Hazard Born of Autumn’s Beauty” on the 23rd).

The beginning of the story:

A Metro-North train uses pressurized water to blast leaf slime off the rails. The sludge can cause train delays and even skidding.

As New York’s canopy shifts to rich hues of red and yellow, it is prime time for leaf peeping. But for Metro-North Railroad employees, the changing colors signal a different occasion: slime season.

Every fall, a gelatinous goo forms on the rails across the Northeast as leaves are crushed by the wheels of passing trains. This slippery leaf slime can cause a train’s wheels to lose traction, slowing them down and leading to delays or, even worse, skidding.

“It can be terrifying,” said Maurice Adams, 39, a Metro-North district superintendent of transportation operations. “You’re coming up to a red signal, meaning you can’t proceed, and you’re sliding and you don’t know if you’re going to stop.”

When trains move through sections of track with leaf sludge, they are required to slow down, which can cause delays. On average, about 250 trains are delayed because of leaf slime per year, according to Metro-North. And if a train hits a slippery patch near a station, it can slip past the platform. It then must reverse to pick up riders, causing more delays. Sometimes trains skid so far past the platform, engineers are ordered to skip the stop and continue on to the next station, Mr. Adams said.

To de-slime the tracks, a team of Metro-North employees uses a custom-made work train that blasts pressurized water onto the rails. During six weeks in the fall — usually from the second week of October until the end of November — four carmen and a foreman (all of whom are men) operate two machines in shifts, up to 20 hours a day, cleaning much of the Harlem and New Haven Lines (up to 200 miles) on a daily basis.

On the compounds leaf slime and leaf sludge: both are subsective Source compounds — ‘slime/sludge made from/of, coming from leaves’ — but referring to specific types of such substances, having their origin in fallen tree leaves, ground into a slime or sludge over time.

On the head nouns, from NOAD:

noun slime: a moist, soft, and slippery substance, typically regarded as repulsive: the cold stone was wet with slime.

noun sludge: thick, soft, wet mud or a similar viscous mixture of liquid and solid components, especially the product of an industrial or refining process

The compounds are not in the OED, which generally doesn’t list semantically transparent combinations, even if they’re attested. The test would seem to be that a combination is both reasonably frequent and at least somewhat specialized in meaning. But actual lexicographic practice is erratic. For X soup Source compounds, for instance, OED has tomato soup, noodle soup, and bean soup, but not mushroom soup, vegetable soup, or chicken soup.

Since the number of distinct (non-repeating) ghits for leaf slime/sludge is quite small — a tiny fraction of the frequency of mushroom soup or chicken soup — it’s no surprise that, despite their contextual specialization, these compounds haven’t made it into the OED. Though in addition to the railroad story, there are a few cites about removing leaf sludge from the gutters of houses:

This means that a bunch of leaves and dirt all along your gutters can add up to hundreds of pounds of leaf-sludge in your gutters. (link)

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