Celtic Religion: Now Available!
This short but coherent work was penned back in one of my favorite eras and styles of literature- the academic theory and archaeological/historical thought of that happy period during the rampant social upheaval of the early technological era- with its tintypes, early moving pictures, and obsession with tombs and temples.
Divided into multiple sections, it has a bit of linguistics, a bit of ancient history, a bit of then-modern archaeology, and plenty of Druidism. While some of its academic content has been largely forgotten these days (especially with regards to its very proto-eugenic view of the progression of civilization) it is still a very good work. It contains a short bibliography with other texts as well for those interested in a larger look at the subject.