The original altar of Saint Mary's is actually encased in the white carrara and red marble of the main altar. This construction happened in the 1890's. Today this altar is used as the Altar of Reservation of the Blessed Sacrament for adoration and for communion taken to the sick.
The newer Altar of Sacrifice at the center of the Sanctuary in front of the Altar of Reservation or High Altar next to the back wall, was added after 1965 to support the liturgical changes established by Vatican Council II.
In this sanctuary were ordained hundreds of priests, many of whom have influenced the early history of the Church in America either as members of the hierarchy or as missionaries.