MIDLAND, TEX., OCT. 15 -- Eighteen-month-old Jessica McClure, trapped 22 feet down an abandoned back yard well since Wednesday morning, talked to her mother, cried and hummed today as rescuers pounded their way through solid rock with jackhammers.

Jessica fell into the well about 9:30 a.m. Wednesday while playing with other children at a private day-care center run by her aunt and her mother.

Early Thursday night, rescuers had drilled a horizontal shaft to within two feet of the toddler, but there was no prediction when they would reach the child because of the hardness of the rock, Midland police Sgt. Jeff Haile told a news conference.

"At some points, it's harder than granite," Haile said, quoting a federal Mine Safety and Health Administration official, Dave Lilly, from Carlsbad, N.M.

Doctors at first said the child could survive as long as 36 hours, or until 9:30 p.m. Thursday, but Dr. Chip Klunick of Midland Memorial Hospital said Thursday night she could survive longer.

"If the child is not injured severely, she could probably go about four days without water," he said. "She is dehydrating, but not at too extensive a rate."

Workers had drilled a 3-by-3-foot shaft 28 feet deep next to the well, then began working up toward the child. Progress was slowed by solid rock that kept breaking drill bits.

Gathered at the site were friends and neighbors who waited and prayed with Jessica's parents, Chip, 18, and Reba Gayle McClure, 17. She is their only child.

Jessica slept during the night after heaters were installed to blow warm air into the 8-inch-wide entrance of the well at her aunt's house. She had not had anything to eat or drink since her fall, and doctors at the scene considered lowering a bottle to her to prevent dehydration.

"But then we thought, we don't want to fill her stomach if she has internal injuries or is going to require surgery when she comes out," Klunick said.

A microphone was dropped into the shaft to communicate with the child, and a camera was lowered so the child's face was briefly visible.

The well, about 8 inches in diameter at the top, widens farther down until it narrows to a 6-inch opening below the spot where Jessica came to rest. The opening had been covered by a large rock or flowerpot which children apparently knocked away.