There is a large volume of information on using skills in 4e D&D. The basic assumption is that the character using the skill is trained and the rules reflect this.
My question is, what about when the character is not trained? Besides not having the extra points for being trained, what are the rules for handling the usage of an untrained skill?
Is there a clear-cut point where the character can not use the Untrained skill?
//* Clarification *//
I know of one example - Arcana Skill. If you are not trained in this you can not do a Detect Magic. Are there others? Maybe even a list somewhere?