Rauskinna - a grimoire by bishop gottskalk 1497-1520; Grskinna - a magical nanuscript, consists of roman alphabet and runic code.

It seems that Rauskinna is a hybrid between ceremonial magic and some kind of galdr.

Both books are mentioned in Galdra-Loftur:

Once there was a student at the Seminary at Hlar. His name was Loftur; he practised magic, and tried to interest others in this practise. Loftur kept to his sorcery studies until he had learned everything contained in the spell-book Grskinna. Then he sought to gain even more hidden knowledge from other sorcerers, but nobody knew more than he did.

arly one winter Loftur spoke to a schoolmate, who was thought to be brave, and asked him to help in calling back to life the ancient bishops. The student did not want to do this, but Loftur threatened him with death if he did not agree. The student asked Loftur how he would be able to help, as he knew no magic. Loftur answered that he was to just stand in the belfry and hold the bell rope. He was forbidden to move at all, but rather was to watch Loftur and then ring the bell as soon as he saw Loftur make a hand signal.

Loftur explained that he wanted to raise the dead because: "Those who have mastered magic in the way I have can only employ it to work evil, and they will surely perish when they die - and yet if one knows enough, the Devil will no longer have any power over a man and must serve him, without getting control over the sorcerer. Anyone who knows that much can use his knowledge as he will. But this knowledge is hard to come by now, ever since The Black School was closed, and Bishop Gottskalk the Evil had the book Rauskinna buried with him. This is why I plan to call him from the dead and get the book from him by magic."
Source

Does anyone know something about these books?