What type of songs were popular at religious revival meetings?

Those would be the spirituals.
The spirituals were very popular during revival meetings and they are most notably known as Negro spirituals as they were songs created by African-Americans about Christianity. They depict Christian values while also telling stories about the evils and hardships that slave had to endure. The spirituals are nowadays considered a distinct and unique genre of music and they are very harmonized.

Religious revival is the process of renewing the life of the church, society or any religious group. Spiritual songs were popular at the religious revival meetings. Some of the popular spiritual songs are Proud Mary, Ramble Tamble, and Long as I Can See the Light.