Catholic monasteries preserve writing from which two ancient group

There's a great book on this subject, in the "Hinges of History" series by Thomas Cahill.  The book is called, "How the Irish Saved Civilization."  It's about Irish monks and the copying they did of ancient documents.  They copied not only Christian documents -- that's one sort of source, and the type of stuff you'd expect from monks.  But they also copied a wide array of ancient pagan documents -- that's another sort of source, and maybe not what you'd expect.  But they were interested in Greek and Latin works of all sorts of writers from antiquity.  Hmm, maybe that would be another "two groups" to your answer -- both ancient Latin and ancient Greek writings, and in both languages both Christian and pagan authors. 

Apocrypha is the answer your looking for