Complex sentence: The school was founded on 14th January 1861, on Mount St. Columba, the building has since went into other use as a retreat and a primary school, Holy Trinity (Previously, St Colmcille), has been the school there since.
Split into simpler sentences: The school was founded on 14th January 1861, on Mount St. Columba. A primary school, Holy Trinity (previously St Colmcille), has been the school there since.