Edited from a variety of translations (mentioned in the preface) by H. R. Percival
The Canons with the Ancient Epitome and Notes.
With regard to the Synod of Gangra we know little beside what we learn from its own synodal letter. Three great questions naturally arise with regard to it.
1. What was its date?
2. Who was the Eustathius it condemned?
3. Who was its presiding officer?
I shall briefly give the reader the salient points with regard to each of these matters.
1. With regard to the date, there can be no doubt that it was after Nice and before the First Council of Constantinople, that is between 325 and 381. Socrates  seems to place it about 365; but Sozomen  some twenty years earlier. On the other hand, Remi Ceillier  inconsistently with his other statements, seems to argue from St. Basil's letters that the true date is later than 376. Still another theory has been urged by the Ballerini, resting on the supposition that the Eusebius who presided was Eusebius of Caesarea, and they therefore fix the date between 362 and 370. With this Mr. Ffoulkes agrees, and fixes the date,  with Pagi, at 358, and is bold enough to add, "and this was unquestionably the year of the Council." But in the old collections of canons almost without exception, the canons of Gangra precede those of Antioch, and Blondel and Tillemont  have sustained this, which perhaps I may call the traditional date.
 Socrat. H. E., Lib. II., cap. xliij.
 Sozomen. H. E., Lib. IV., cap. xxiv.
 Remi Ceillier. Hist. Générale des Auteurs Sacrés, Tom. IV., p. 735.
 E. S. Ffoulkes, in Smith and Cheetham, Dict. Christ. Antiq., s. v. Gangra.
 I am indebted to Hefele for this reference, and he gives Mémoires, note xxvij., sur St. Basile.
Reference address : https://www.elpenor.org/ecumenical-councils/gangra.asp