Complex sentence: The high altar of the unfinished cathedral was consecrated on December 21,1906, in a private ceremony, and the first Pontifical High Mass at the new cathedral took place on December 25,1906.
Split into simpler sentences: The high altar of the unfinished cathedral was consecrated on December 21,1906, in a private ceremony. The first Pontifical High Mass at the new cathedral took place on December 25,1906.