She was of a very light-hearted and joyous disposition, always contented and happy, singing like a nightingale at her work all the day long, when she was alone, and cheering and enlivening all around her by her buoyant spirits when she was in company.

When Mary Bell became old enough to run about and play, Mary Erskine became her playmate and companion, as well as her protector.

There was no distinction of rank to separate them.

If Mary Bell had been as old as Mary Erskine and had had a younger sister, her duties in the household would have been exactly the same as Mary Erskine's were.

In fact, Mary Erskine's position was altogether that of an older sister, and strangers visiting, the family would have supposed that the two girls were really sisters, had they not both been named Mary.
Mary Erskine was about twelve years older than Mary Bell, so that when Mary Bell began to go to school, which was when she was about five years old, Mary Erskine was about seventeen.