stone walls are crumbling

[Loriann]

[size=18]I live in an old house (circa 1920) with a stone walled basement. I run a dehumidifier all year round in the laundry area. I was recently sweeping cobwebs from the walls, and sweeping the floor, when little chunks of crumbled stone began falling from the walls. Am I keeping it too dry in there, or is it the result of too much humidity? In summer the basement is quite humid, and I keep 2 dehumidifiers running, one in the laundry room and one in the play room.