Alas, some aspects of the novel haven't aged well. The N word is used (though never approvingly) and racist attitudes are well to the fore, albeit with the explicit disapproval of the author. Jacob is dressed up as a monkey, his black hands are regarded as dirty by the servants etc; but his character is utterly admirable, he is brave, resourceful, loyal and inventive, and his friendship with intelligent, adventurous, blind Susan is delightful. On the other hand, the description of the gypsies at the very end of the book has no redeeming qualities; the sympathy and understanding extended to Jacob apparently doesn't apply to these stereotypical villains.
Despite these reservations, I still thoroughly enjoy Chimneys and the interweaving of past and present: Tolly's part in the rescue of young Boggis which I mentioned above, the way Susan and Jacob in 1799 hear 'the ghost boy' Tolly singing his sea shanties in the treetops a hundred and fifty years later. The relationship between Tolly and his great-grandmother is lovely, and the motif of the quilt patches which tie past and present together is clever and satisfying. One of my favourites of all time.
(I first read Chimneys as a child in colonial PNG. I think, I hope, that the portrayal of quick-witted, fierce Jacob helped to counteract the racist attitudes to the 'locals' that surrounded me every day.)