The sort of vocabulary that you would expect the simple folk of the Dark Ages to be using are mostly still of Germanic origin; they are the building blocks of the language, the basics of verb and noun forms, and words for basic abstract concepts.
In later years, the Catholic Church's supremacy meant that the language of inquiry, knowledge, and spirituality was Latin. For many centuries, scientists would publish all their work in Latin. It is no surprise that Latin has filled the gaps in English and provided adjectives such as lunar where English had none.
This is compounded by the imposition of Norman French in the Middle Ages. Since the language of government changed from English, many of our words for government and justice derive from Latin via Norman French. Our words for meats also come from Norman French, e.g. beef, veal, venison, mutton in place of English cow, calf, deer, sheep.
Later still, British scholars would turn to Latin and Greek to coin new words to describe new technologies and modern concepts, as we still do today.
There's an interesting discussion of the influence of Latin on English on wikipedia here: http://en.wikipedia.org/wiki/Latin_influence_in_English