Coruscation

In Montclair, NJ, where there is a concerted emphasis on thinking of the town as one diverse whole -- children are bused to "magnet" schools, and the moniker "Upper" is discouraged as divisive -- several agents resisted comparisons of trends on the two sides of town.

"Sometimes people come in saying they only want to buy in the one ZIP code, 07043," said Linda Grotenstein, an agent at Coldwell Banker. "I usually find they have a misunderstanding of what the ZIP codes imply."

The housing stock is more homogeneous in the northern half: mostly well-groomed Victorians with three to six bedrooms. The south end has far greater range: everything from run-down, run-of-the-mill triplexes on narrow lots to peerless mansions on manicured grounds, in the "estate section."

In fact, by Mr. Baris's reckoning, the estate section in the southern part of Montclair has kept overall average sales value afloat. It had 42 listings this year, and 18 houses sold, at a median price of $1.218 million, 31 percent more than last year.

"If you took out the estate section," Mr. Baris said, "Montclair would have depreciated as a town."

In Millburn/Short Hills, Ms. Bigos ascribes the huge price disparity to the teardown craze that swept Short Hills starting in the late 1990s.

"That is when the spread started to widen," said Ms. Bigos, a lifelong resident of Short Hills. "All the new houses going up doubled and tripled in value."

Both Millburn and Montclair have Midtown Direct New Jersey Transit train service to Manhattan, which various reports have shown can increase property value by as much as 20 percent. Millburn has had it for 15 years, while the service arrived in Montclair seven years ago.