You said "I know that this name changed spelling the farther you go back. I think Van Slyke is the americanized version."
It is very true that the spelling of names changed over the centuries. Spelling was phonetic and very often the person giving the info could not spell, so could not "correct" the person writing it down. Often the person taking the info also could not spell.
The Van Slyke name was one of the few Dutch "surnames" that was an established surname long before Cornelis Antonissen arrived in the New World in 1634. Most often the Dutch in the New World used the patronymic system of naming before the 1680s. See my article on this at http://www.rootsweb.com/~ote/http://www.rootsweb.com/~ote/
(Select NEW NETHERLAND at the main menu, then choose Dutch Naming Patterns)
Surnames were not commonly used before 1660, and individuals were distinguished from others of the same first name by their place of origin, their father's name, a physical characteristic, their occupation or a nickname.
In old Dutch, the letters "y" and "ij" were used nterchangeably and Slijk could be written as Slyk or Slyck. The earliest record found of the place name Slijck is from 25 March 1424 when Heer Wouter van Mijnden and van Ruwiel conveyed land "on Slijck in Maerssen" to two Utrecht convents.It also emerged early as a last name when Splinter Egbertsz. van den Sliick placed his seal as a "landgenoot" of Galecop in 1441.
Cornelis has been found in the records under a variety of names (and spellings). The Van Slyke name is not a common one in present-day Netherlands, and a check of the Netherlands phone book reveals less than two dozen with the following spelling variations: Slijk, Van Slyke, Van Slijk, Van Slyken and Van Slijcken.