The word "miracles" is the Greek word "semeion" which means "signs." 1 Corinthians 14 says that speaking in tongues is a sign - a "semeion." Paul and Barnabas shared with the apostles and elders all that God had been doing with them among the Gentiles. The greatest thing that the apostles and elders would have believed would have been speaking in tongues. When the apostles at Jerusalem had been born again on the day of Pentecost they had spoken in tongues. That was the "sign" that they had received holy spirit. Paul and Barnabas shared both the doctrine of the grace of God that they had been teaching and the resulting signs and wonders. They had shared these same things on the way to Jerusalem and after they arrived. From the context it is evident that the council accepted that which Paul and Barnabas shared about the signs and wonders. There was no further argument in the council after this.
To conclude the matter James the half-brother of Jesus who was leading the church at this time gave his sentence. It is an important presentation both for what it says regarding the gospel of the grace of God and also for what it does not say.
Gladly
Acts