If you’re walking on Elliott Way, south of the Yacht Club, you’ll see some red bricks scattered among the rip rap along the shore. These all appear to be what were called Croton Point bricks, made at the William A. Underhill Brickyard on the northern end of the point. Some Underhill bricks were stamped with his initials (WAU) but others, like the partial example shown above, were stamped IXL, a clever bit of self-promotion meaning “I excel” at brickmaking.
During the height of the brickmaking industry in the 1850s there were more than 25 brickyards on the shores of Haverstraw Bay and in Croton there were five in the area between what is now Half Moon Bay and the end of Croton Landing Park.1
For some nice examples of WAU bricks see this post, History Underfoot.
- United States Coast Survey. Hudson River No. VI, Topographical Survey by F.H. Gerdes. August, 1854. ↩︎
CROTON 
When the tide is low at George’s Island, you can see thousands of bricks, with assorted makers’ marks.
There was a large brickyard there in the 1850s.
XL was also the name of a banking code used to encrypt communications with smuggling ships from Montauk Point past Long Beach and into Albion and Highlands NJ just north of Atlantic City in 1929. Bank of America and others were indicted and the entire case–docks, observatory, radio station, mansion, tunnels–disappeared from the press after November 1929. –Libertariantranslator