A contractor came today and took measurements down the chimney, on the outside wall and into the basement. I sure want him working for me because the first cement block removed in the basement was exactly where the cat was located. A trip to the vet revealed slight dehydration but otherwise okay. My friend's husband has enclosed the chimney top with hardware cloth so this tragedy won't happen again with any other living creature. I wish it were an indoor-only cat but that isn't my call to make. It has used some of it's 9 lives but all is now well. Thanks so much to all for your concern and suggestions.