N.J. Stat. § 26:6-36
Every dead body interred in any burial ground or cemetery in this state shall be buried so that the top of the outside coffin or box shall be at least four feet below the natural surface of the ground, and shall be immediately covered with at least four feet of earth, soil or sand.
Bodies of infants in coffins or boxes not more than four feet in length shall be buried so that the top of the outside coffin or box shall be at least three feet and six inches below the natural surface of the ground, and shall be immediately covered with at least three feet and six inches of earth, soil or sand.
This section shall not apply where bodies are placed or buried in properly constructed private vaults so as to prevent the escape of noxious or unhealthy gases therefrom.
N.J.S. § 26:6-36