Also, "old" doesn't per force imply "outdated". Especially in ecology (or, as it was known, natural history), there's a lot of good work that was done in the 19th century that would deserve much wider attention today.

Just yesterday I was identifying a species of African ant. As I researched it, I found myself using taxonomic keys and descriptions published between 50 and 150 years ago - in English, French, German and Latin! Fortunately they had been digitized, and at least partially translated...