Georgia Code Title 9. Civil Practice § 9-11-43

(a) Evidence on trials.In all trials the testimony of witnesses shall be taken orally in open court unless otherwise provided by this chapter or by statute.

(b) Evidence on motions. When a motion is based on facts not appearing of record, the court may hear the matter on affidavits presented by the respective parties, but the court may direct that the matter be heard wholly or partly on oral testimony or depositions; provided, however, that this provision shall not limit the right of parties to use depositions where they would otherwise be entitled to do so.

(c) Determination of the law of other jurisdictions.A party who intends to raise an issue concerning the law of another state or of a foreign country shall give notice in his pleadings or other reasonable written notice. The court, in determining such law, may consider any relevant material or source, including testimony, whether or not submitted by a party or admissible under the rules of evidence. The court's determination shall be treated as a ruling on a question of law.